GIFT  OF 


Al 


AIRPLANES  IN  ACTION. 


GENERAL  SCIENCE 

A  BOOK  OF  PROJECTS 


BY 

EDGAR  A.   BEDFORD,  Sc.D. 

HEAD   OF   THE   DEPARTMENTS   OF   BIOLOGY   AND  GENERAL   SCIENCE 
DE  WITT   CLINTON    HIGH   SCHOOL,    NEW   YORK   CITY 

LECTURER   ON    METHODS    IN   TEACHING   GENERAL    SCIENCE 
DEPARTMENT   OF   PEDAGOGY,    NEW   YORK   UNIVERSITY 


ALLYN   AND   BACON 

BOSTON  NEW   YORK  CHICAGO 

ATLANTA  SAN    FRANCISCO 


COPYRIGHT,  1921 
BT  EDGAR  A.  BEDFORD. 


PREFACE 

THE  material  of  General  Science  is  organized  according  to 
the  project-problem  plan.  The  class  projects  are  broken 
up  into  problems,  in  the  solution  of  which  the  pupils  are 
led  to  form  hypotheses  from  their  observations,  to  check 
and  modify  these  hypotheses  by  further  observations,  and 
finally  to  come  to  a  conclusion  which  is  of  value  in  the 
development  of  the  project. 

The  following  aims  have  been  kept  in  mind : 

First :  to  encourage  the  spirit  of  inquiry,  and  to  cultivate 
the  attitude  of  independent  judgment,  of  opemninded- 
ness,  and  of  reliance  upon  facts. 

Second:  to  put  the  pupils  in  possession  of  certain  funda- 
mental truths  which  give  an  explanation  of  many 
everyday  activities. 

Third:  to  lead  pupils  to  a  broad  view  of  the  forces  that 
affect  their  surroundings,  rather  than  a  detailed  study 
of  some  one  section  of  their  environment.  The  pupils 
of  this  early  adolescent  period  are  interested  in  big 
units  and  a  broad  outlook,  rather  than  in  minute 
details. 

The  material  has  been  selected  from  that  part  of  the 
environment  which  is  related  to  the  practical  interests  of 
the  pupils.  No  material  has  been  included  merely  because 
it  helps  in  developing  some  scientific  generalization.  The 
needs  of  the  ordinarily  well-educated  citizen,  rather  than  the 

45^963 


iv  PREFACE 

needs  of  the  scientist,  have  influenced  the  choice  of  topics. 
Preference  has  been  given  to  topics  which  lead  to  the 
understanding  of  phenomena  of  large  economic  importance. 

The  environment  has  been  considered  as  a  whole,  not  as 
made  up  of  divisions  which  can  be  classified  as  physics, 
chemistry,  biology,  astronomy,  and  physiography.  In 
working  out  a  problem  for  the  solution  of  the  project,  use 
is  made  of  any  necessary  facts,  regardless  of  whether  they 
belong  to  this  or  that  special  division  of  science. 

By  means  of  a  large  number  of  suggested  individual 
projects,  the  teacher  is  enabled  to  adapt  the  course  to  his 
special  school.  Pupils  are  encouraged  to  work  out  the 
projects  that  are  of  the  most  interest  to  them.  Not  all 
that  are  listed  are  to  be  required  of  any  one  student.  Some 
are  so  simple  that  any  one  can  perform  them  easily,  while  a 
few  appeal  only  to  those  who  have  a  decided  mechanical 
bent. 

The  text  carries  out  the  spirit  of  the  recommendations 
as  to  general  science  of  the  Commission  on  the  Reorgani- 
zation of  Science  in  the  Secondary  Schools  It  is  adapted 
for  use  in  the  junior  high  school,  or  in  the  first  year  of  the 
high  school. 

The  author  wishes  to  express  his  appreciation  to  many 
friends  and  fellow  teachers  whose  assistance  has  contributed 
much  in  the  preparation  of  this  book.  Mr.  Harry  G. 
Barber,  Department  of  Biology,  and  Mr.  Thomas  Curry, 
Chairman  of  the  Department  of  Physics,  in  the  De  Witt 
Clinton  High  School  New  York  City,  have  read  much  of 
the  manuscript  and  have  made  helpful  suggestions  and 
criticisms.  The  following  teachers  of  general  science  in 
the  New  York  City  schools,  acting  with  the  author  in 
planning  a  syllabus  in  general  science,  have  given  much 
valuable  advice:  Mr.  Maurice  W.  Kearney,  Bay  Ridge 


PREFACE  v 

High  School;  Dr.  Elsie  M.  Kupfer,  Wadleigh  High  School; 
Miss  Mary  Morris,  Newtown  High  School;  Miss  Ethel 
Schwarz,  Speyer  Experimental  Junior  High  School;  Miss 
Emily  Topp,  Julia  Richman  High  School ;  and  Dr.  George 
C,  Wood,  Commercial  High  School. 

Mr.  George  K.  Gombarts,  Head  of  Art  Department,  and 
Mr.  John  W.  Tietz  of  Department  of  Biology,  De  Witt 
Clinton  High  School,  have  given  valuable  advice  concerning 
illustrations  and  have  furnished  original  drawings  and 
photographs. 

Dr.  Charles  F.  Brooks  of  the  Weather  Bureau,  Dr.  L.  O. 
Howard,  Chief  of  the  Bureau  of  Entomology,  and  Mr.  W. 
B.  Greeley,  Chief  of  Forest  Service,  have  been  generous  in 
opening  the  resources  of  their  departments. 

Superintendent  Clarence  E.  Meleney,  Superintendent  John 
L.  Tildsley,  and  Dr.  Francis  H.  J.  Paul,  Principal  of  De  Witt 
Clinton  High  School,  by  their  broadness  of  view  and  edu- 
cational vision,  have  been  sources  of  stimulation  in  the 
development  of  the  course  represented  in  the  book. 

To  his  wife,  Leila  Hoge  Bedford,  the  author  desires 
especially  to  express  his  indebtedness  for  her  intelligent 
and  painstaking  assistance. 

E.  A.  B. 


TABLE  OF  CONTENTS 

Suggested  individual  projects,  reports,  and  references  are  not  listed  here,  but 
may  be  found  at  the  end  of  most  projects. 

UNIT   I 
RELATION  OF   AIR  TO  EVERYDAY -ACTIVITIES 

PAGE 

PROJECT  I.    IMPORTANCE  OF  THE  WEIGHT  OF  AIR         .  •       .       1 

Problem  1.  How  an  airplane  remains  in  the  air                .1 

2.  Has  air  weight?    ...         .         .         .      4 

3.  Does  air  press  upon  things  ? .         .         .         .5 

4.  How  air  pressure  may  be  measured       .         .6 

5.  Why  water  is  not  used  in  making  barometers      7 

6.  How  an  aviator  knows  how  high  he  is  .         .       9 

7.  Why  air  pressure  does  not  prevent  us  from 

lifting  objects     .'.•-.•        .         .         .         .9 

8.  Why  a  balloon  or  dirigible  remains  in  the  air     10 
PROJECT  II.    How  WE  USE  COMPRESSED  AIR       .    .     .         .17 

Problem  1.      How  air  pressure  is  used  in  building  founda- 
tions and  subways         .         .  .17 

2.  How  compressed  air  is  used  in  automobile 

tires       .         .         .         ....      .         .         .19 

3.  How  the  tire  pump  works     .         .         .         .20 

4.  How  a  force  pump  sends  a  steady  stream  of 

water     ....  .     22 

PROJECT  III.    VENTILATION    .         .                          •         •  .25 

Problem  1.     Why  rooms  should  be  ventilated  .         .  .25 

2.  How  air  in  a  room  may  be  set  in  motion  .     27 

3.  How  convection  currents   may  be  used  in 

ventilating  a  room      ••'  v        .  .     29 

PROJECT  IV.    WINDS       .       '.        .        .        .         .         .         -31 

Problem  1.     How  sea  breezes  are  caused  .  .31 

2.  Why  our  winds  vary  in  direction  and  velocity     33 

3.  What  are  hurricanes  ?    .         .         .  .38 

4.  How  the  weather  bureau  is  able  to  predict 

the  weather  .         ...  .42 

vii 


viii  TABLE  OF  CONTENTS 

PAGE 

J.    How  WE  HEAR 44 

Problem  1.    What  sound  is  .        .        .        .        .44 

2.  How  a  phonograph  reproduces  sound    .        .    47 

3.  How  the  ear  is  fitted  to  receive  sounds          .     50 

PROJECT  VI.    IMPORTANCE  TO  Us  OF  OXIDATION  (BURNING)     54 

Problem  1.  What  burning  is    ;         .         .         .         .         .54 

2.  How  the  power  of  an  automobile  is  produced     57 

3.  How  a  match  is  lighted         .         .         .         .58 

4.  What  causes  iron  to  rust       .         .     \-  .,.       .     60 

5.  Why  coal  is  burned       .        .        .        .        .63 

6.  How  available   energy  is    supplied  to   the 

human  body          .        .        .        .        .65 

7.  Do  plants  breathe?       ..        .'        .        .        .67 

8.  How  animals  take  in  oxygen  and  give  off 

carbon  dioxide       .         -.'••"       •         .69 

PROJECT  VII.    PREVENTION   OF  DESTRUCTIVE  BURNING  OR 

OXIDATION        .      -  .        .   •     .      •  .        .74 
Problem  1.    How  destructive  oxidation  may  be  prevented 

by  excluding  the  air      .    .     .        .        .75 

2.  How  destructive  oxidation  may  be  prevented 

by  reducing  the  temperature  below  the 
kindling  point        .  " '. .    .  ;  I     .         .         .     77 

3.  How  destructive  oxidation  may  be  prevented 

by  removal  of  fuel  material  .        .        .    77 

PROJECT  VIII.    IMPORTANCE  TO  Us  OF  THE  OTHER  GASES  OF 

THE  AIR   .       '  .- r  "    V '""     •     I  •        •        •    80 
Problem  1.     Does  air  contain  any  gas  besides  oxygen?     .     80 

2.  How  much  of  the  air  is  oxygen?    .        .        .80 

3.  Importance  of  nitrogen  in  the  air  .         .         .     81 

4.  Importance  of  carbon  dioxide  of  the  air        .    82 

PROJECT  IX.    To  KEEP  FOODS  FROM  SPOILING     .        .        .92 
Problem  1.     What  causes  foods  to  spoil  or  decay?   .        .     92 

2.  Where  bacteria  are  found      .         .         .         .93 

3.  Size,  shape,  and  method  of  multiplication  of 

bacteria 95 

4.  What  conditions  are  favorable  and  what  un- 

favorable for  growth  of  bacteria  and 
molds?  96 


TABLE  OF  CONTENTS  ix 

PAGE 

Problem  5.    Use  of  cold  in  the  home  in  checking  the 

growth  of  bacteria         .        .        .        .97 

6.  Use  of  cold  in  storage  warehouses        .        .     100 

7.  Use  made  of  heat  in  food  preservation        .     103 

8.  Use  made  of  other  methods  of  food  preser- 

vation  104 

PROJECT  X.    To  PROTECT  OURSELVES   AGAINST  HARMFUL 

MICROORGANISMS 108 

Problem  1.    How  bacteria   and   other   microorganisms 

affect  the  health  .        .        .        .        .108 

2.  How  disease  germs  may  pass  from  one  per- 

•  son  to  another     .         .         .         .         .     Ill 

3.  How  the  body  fights  disease        .        .        .113 

4.  How  the  body  acquires  special  power  to 

fight  disease 115 

5.  Use  of  disinfectants  and  antiseptics     .        .119 

PROJECT  XI.    To    FIND   OUT  How   SOME    BACTERIA   AND 

MOLDS  ARE  USEFUL      .        .        .        .122 
Problem  1.     Are  bacteria  of  decay  of  any  value  ?    .        .     122 

2.  How  bacteria  on  the  roots  of  some  plants 

may  enrich  the  soil .  ...     123 

3.  How  bacteria  are  useful  in  other  ways         .     125 

UNIT   II 
RELATION  OF  WATER  TO  EVERYDAY  ACTIVITIES 

PROJECT  XII.    MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE 

TO  Us     .        .     ., ..;•:     ....  127 

Problem  1.    How  dew  is  caused 127 

2.  How  fogs  and  clouds  are  produced      .        .  131 

3.  How  rain,  snow,  and  hail  are  formed  .         .132 

4.  Reasons  for  unequal  distribution  of  rainfall  134 

5.  How  water  is  supplied  to  dry  areas     .        .  136 

6.  How  moisture  gets  into  the  air    .        .        .  138 

7.  How  the  amount  of  moisture  in  the  air 

affects  our  comfort          V       .     .         .     142 

PROJECT  XIII.    THE  RELATION  OF  PLANTS  TO  MOISTURE  .     144 
Problem  1.     Do  plants  give  off  moisture?  .    v     <•  ,      -*;  144 


X  TABLE  OF  CONTENTS 

PAGE 

Problem  2.    The  amount  of  water  given  off  by  plants    .     145 

3.  How  the  root  system  of  a  plant  is  fitted  to 

find  water    .         .      .  ;.        .   '      .         .     145 

4.  How  roots  are  especially  fitted  to  take  in 

moisture      .         .     :   »        ....      .         .     146 

5.  How  root  hairs  take  in  water       .        .        .     148 

6.  How  water  passes  out  of  the  leaves     .        .     149 

PROJECT  XIV.    WATER  POWER     .        .        ...        .152 

Problem  1.    What  is  the  source  of  energy  of  water  power  ?     153 
2.     Source  of  the  power  of  hydraulic  pressure  .     157 

PROJECT  XV.    To  UNDERSTAND  How  COMMUNITIES  OBTAIN 

A  GOOD  SUPPLY  OF  WATER    .        .        .     160 
Problem  1.    Why  a  wooded  mountainous  region  is  se- 
lected to  furnish  water         .  .161 

2.  How  the  water  is  protected          .        .        .     164 

3.  How  other  cities  obtain  a  supply  of  water  .     166 

4.  How  the  water  system  within  the  house 

should  be  cared  for      .         .        .        .     168 

PROJECT  XVI.    To  UNDERSTAND  THE  DISPOSAL  OF  SEWAGE 

OF  .HOMES  AND  COMMUNITIES      .  .  •  :     .     171 
Problem  1.     Care  of  waste  water  pipes    .        .        .        .     171 

2.  Sewage  disposal   in   villages   and    isolated 

houses          .        .        .        ..••':  .-•        -     171 

3.  Sewage  disposal  in  cities      .        :.        .        .     172 

PROJECT  XVII.    WATER  AS  "A  MEANS  OF  TRANSPORTATION     175 
Problem  1.    How  New  York  harbor  originated       .         .175 

2.  Effect  of  the  forests  of  the  Adirondacks  upon 

New  York  harbor  and  the  navigability 

of  the  Hudson  River    .        .        .        .178 

3.  Importance  of  internal  waterways       .        .182 

4.  How  ocean  transportation  depends  upon 

science  186 


UNIT  III 

THE  RELATION  TO  US   OF  SUN,   MOON,  AND  STARS 
PROJECT  XVIII.    To  UNDERSTAND  THE  CAUSE  OF  TIDES   .     191 


Problem  1.    What  causes  the  water  to  rise 


192 


TABLE  OF  CONTENTS 


XI 


PAGE 

Problem  2.  Why  there  are  two  high  tides  a  day    .        .195 

3.  Why  high  tide  is  a  little  later  every  day     .     196 

4.  Why  the  moon  does  not  fall  to  the  earth     .     197 

5.  Why,  at  times,  there  are  especially  high  tides     199 

6.  Why  sometimes  only  a  portion  of  the  moon 

is  visible  to  us          .  .        .         .201 

PROJECT  XIX.    How  TO  KNOW  SOME  OF  THE  FIXED  STARS    205 
Problem  1.    How  to  recognize  the  constellations  around 

the  north  pole      .....     205 
2.    How  to  recognize  the  constellations  seen  only 

hi  winter      ...        .        .        .     207 

PROJECT  XX.    TIME  AND  SEASONS       .  .     .        .        .        .    211 

Problem  1.    Why  we  have  winter  and  summer       .        .211 

2.  Why  July  and  August  are  the  hottest  months 

and  January  the  coldest  month  .        .     213 

3.  How  time  is  calculated        ....     214 

4.  How   places    on   the   earth's   surface   are 

indicated  217 


UNIT  IV 
WORK  AND  ENERGY 

PROJECT  XXI.    THE  SUN  AS  A  SOURCE  OF  ENERGY  .        .  219 
Problem  1.    How  the  sun's  energy  is  used  in  making 

pictures 221 

2.  Other  chemical  changes  produced  by  the 

sun's  energy 223 

3.  How  direct  use  may  be  made  of  the  sun's 

energy 223 

4.  How  the  energy  of  the  sun  is  maintained    .  225 

PROJECT  XXII.    MACHINES .228 

Problem  1.    What  is  meant  by  work  and  force         .        .  228 

2.  How  work  and  force  are  measured       .         .  229 

3.  Reasons  for  using  machines         .         .         .  230 

4.  How  the  lever  is  used  in  doing  work  .        .231 

5.  How  wheels  are  used  in  doing  work    .        .  233 

6.  Why  pulleys  are  used           .         .      ,  .         .  235 

7.  How  inclined,  planes  are  used  in  doing  work  238 

8.  Why  machines  are  not  100  per  cent  efficient  241 


Xll  TABLE  OF  CONTENTS 

PAGE 

9.     How  friction  may  be  reduced       .      '  .    ,     .  242 

10.  Is  friction  ever  useful  .         .         .   .     .         .  243 

11.  Causes  of  inefficiency  of  engines  .      •   •         •  245 

12.  The  working  of  the  gas  engine     .     ,  Y        .  246 

PROJECT  XXIII.     ELECTRICITY  AND  MODERN  LIFE      .         .  252 

Problem  1.     How  the  electric  bell  rings  .         .     -.'>;.       .  253 

2.  How  magnets  are  used      •  .     '    .      y.'J      .  255 

3.  How  chemical  energy  may  be  changed  into 

electrical  energy 257 

4.  How  electricity  is  measured :  volts,  amperes, 

kilowatts      .       •.      '  v       .    •     .        .  259 

5.  Use  of  induction  coil  in  wireless  telegraphy 

and  in  the  production  of  spark  in  gaso- 
line engine   .        .        ;        .        .         .  261 

6.  How  mechanical  energy  is  changed  into  elec- 

trical energy  by  the  dynamo        .         .  262 

7.  How  electrical  energy  is  changed  into  me- 

chanical energy  by  the  electric  motor .  265 

8.  How  electroplating  and  electrotyping  are 

done -.  266 

9.  How  heat  is  produced  by  electricity    .         .  267 

10.  How  electric  lights  are  produced          .         .  268 

11.  How  the  " storage  battery"  is  used     »  y     .  271 

12.  How  lightning  is  produced  .      •  \        >  ;,      .  273 

PROJECT  XXIV.    RELATION  OF  LIGHT  TO  OUR  ABILITY  TO 

SEE  THINGS 276 

Problem  1.    How  objects  are  visible       ....  276 

2.  Cost  of  artificial  lighting  of  rooms       .         .  278 

3.  Why  shades  and  reflectors  are  used     .         .  282 

4.  How  the  color  of  the  wall  affects  the  lighting 

of  a  room 285 

5.  Why  objects  have  different  colors        .        .  286 

6.  What  is  the  cause  of  the  colors  of  sunset  and 

sunrise  and  of  the  blueness  of  the  sky  ?  287 

7.  Why  eyeglasses  are  used  by  some  persons  .  288 

8.  Advantage  of  having  two  eyes     .         .        .  293 

9.  How  eyes  may  be  injured    .         .         .         .  293 

10.  How  a  lens  makes  objects  appear  larger      .  294 

11.  How  motion  pictures  are  produced      .         .  295 


TABLE  OF  CONTENTS  xiii 


Problem  12.     How  light  effects  may  guide  us  in  the  selec- 
tion of  clothing    .         .         .     '    .         .  297 
PROJECT  XXV.    IMPORTANCE  OF  HEAT  TO  Us     .        .  .      .  300 
Problem  1.    How  a  thermos  bottle  keeps  hot  liquids  hot 

and  cold  liquids  cold   ....  300 

2.  How  food  may  be  cooked  in  a  fire  less  cooker  30 1 

3.  What  substances  are  good  and  what  are 

poor  conductors  of  heat       .         .         .  302 

4.  How  houses  are  heated  304 


UNIT  V 

RELATION  OF  SOIL  AND  PLANT  LIFE  TO  EVERYDAY 
ACTIVITIES 

PROJECT  XXVI.  How  SOIL  Is  MADE          .        .        .        .  308 

Problem  1.  Of  what  is  soil  composed  ?  ....  309 

2.  Evidence  that  soil  is  now  being  formed        .  310 

3.  How  soil  has  been  produced  by  weathering  311 

4.  How  soil  has  been  produced  by  water  and 

wind  erosion      ..         ....     313 

5.  How  most  of  the  soil  of  northern  United 

States  has  been  produced    .  .     314 

6.  How  soil  has   been  produced  by  decay  of 

organic  matter     .  .        .        .318 

PROJECT  XXVII.    RELATION  OF  SOIL  TO  PLANTS  .    321 

Problem  1.    How  the  water-holding  power  of  the  soil 

may  be  increased  '    •;      «'       •     321 

2.  What  plants  take  from  the  soil    . 

3.  How  nitrogen  may  be  given  to  the  soil        .     324 

4.  How  potassium  and  phosphorus  are  supplied 

to  the  soil     .  •  •     325 

5.  How  plants  remove  needed  materials  from 

the  soil      ...  -326 

6.  What  plants  do  with  material  taken  from 

the  soil    .     .  -327 

PROJECT  XXVIII.  How  PLANTS  AND  ANIMALS  MAKE  USE 
OF  THE  FOOD  MANUFACTURED  BY 
PLANTS  .  •  •  -  329 


XIV 


TABLE  OF  CONTENTS 


PAGE 

Problem  1.     Why  must  plants  and  animals  have  food?  .  329 

2.  What  foods  are  good  for  fuel,  and  what  ones 

for  growth  and  repair  ....  330 

3.  How  the  fuel  value  of  foods  is  measured     .  333 

4.  What  is  the  proper  amount  of  food  ?    Table 

of  100  Calorie  Portions  .         .         .         .336 

5.  What  considerations  should  govern  the  plan- 

ning of  our  diet  ? .         .         .         .         .  342 

6.  Why  must  foods  be  digested?      .        .        .  343 

7.  How   can    we    prove    that    nutrients    are 

digested? 345 

8.  Where  is  food  of  the  human  body  digested?  346 

PROJECT  XXIX.    How  PLANTS  PRODUCE  SEED  .       v-      .  349 

Problem  1.     Why  plants  produce  seed     ....  349 

2.  What  are  the  parts  of  a  seed?     .        .         .  349 

3.  Where  seeds  are  produced    .        .        .        .  352 

4.  Do  ovules  always  develop  into  seeds  ?          .  -  353 

5.  How  the  pollen  grain  influences  the  develop- 

ment of  the  ovule  into  the  seed    .         .  354 

6.  Does  it  make  any  difference  whether  the 

pollen  comes  from  the  same  flower  or 

a  different  one?            .•  ^    .        .        .  355 

7.  How  self-pollination  is  prevented         .        .  356 

8.  How  pollen  is  carried  from  one  flower  to 

another     •  '*         .         .        .         .         .  357 
PROJECT  XXX.    How  BETTER  PLANTS  AND  ANIMALS  ARE 

PRODUCED    .        .  ::    .»,.      ,  •:      .        .  362 
Problem  1.    Have  we  evidence  of  improvement  of  plants 

and  animals  during  past  generations  ?  362 

2.  How  plants  and  animals  may  be  improved 

by  selection          .        .                 .     *-"' .  363 

3.  How   more    rapid    improvement    may   be 

brought  about     .        .        .         .        .  364 

PROJECT  XXXI.    INSECT  ENEMIES  OF  PLANTS    .        .        .  369 

Problem  1.     How  insects  are  injurious  to  plants     .     *   .  369 

2.  How  injurious  insects  may  be  destroyed      .  372 

3.  How  the  number   of   injurious   insects   is 

reduced  by  natural  means  .        .        .  375 

APPENDIX                                                             *       .        .  381 


LIST  OF  ILLUSTRATIONS 

FIGURE  PAQE 

Airplanes  in  Action  .  .       ^>u,  -      -.  .     Frontispiece 

1.  Sectional  View  of  an  Airplane .        .       r,        •        •  •      2 

2.  Airplane  in  Air         .         .         .        y        ,         .         .  .       3 

3.  United  States  Airplane     .      .  .*        •     :>\^  -4 

4.  Weighing  Basket  Ball  Inflated  with  Air  .  .5 

5.  Weighing  Basket  Ball  after  Air  Has  Been  Exhausted  .      5 

6.  Simple  Barometer    .         .     ...,».    :,,..-.              •  •       6 

7.  Mercurial  Barometer         .        ,        ..;,,.;  -.:.:     .         .  .       7 

8.  Aneroid  Barometer  .         .                ..         .      -.,.      .  .       8 

9.  Diagram  of  an  Aneroid  Barometer 9 

10.  Inverting  a  Glass  Filled  with  Water         .        .        .  .10 

11.  French  War  Balloon       ;..,.,...     .         ...     10 

12.  Making  Hydrogen   ...  .  ,. 

13.  Drawing  Up  Ink  into  a  Medicine  Dropper    •       >  .     11 

14.  Pouring  Liquid  from  a  Small  Opening  in  a  Can        .  .     12 

15.  Relative  Size  of  Chest   Cavity  during  Inspiration  and 

Expiration          .,      .        .        .        •        •        •  .12 

16.  Non-skid  Automobile  Tire        .   .     *     , ....  . .-.;-•'.• 

17.  Sole  of  Basket  Ball  Slipper      ;..        ••-.•;            •;•    :  •     13 

18.  Suction  Pump           .         .         .        .      ..-.         .        .  •     14 

19.  Siphoning  Liquid  from  a  Barrel        .         ;         .     T-\4^  •     14 

20.  An  Inverted  Drinking  Glass  Pushed  Down  into  Water  .     17 

21.  Caisson     .         .         .      ".  |     .         .         .         .     :  ;^;:-  .     18 

22.  Bicycle  Pump  ....         ,     ;.  ,.•       .      ^|  .     21 

23.  Force  Pump      .         .         .     ,    .        .',» ''.'•..  /     .  .      ..  .     21 

24.  Compressed  Air  Drills      .        .....     .  ,.     :    .  -     22 

25.  Riveting  Hammer   /.        .        .        »-..        *        .  .     23 

26.  Electric  Fan    •-:'. ..      .     '   .        .        ....      ,     . -i  '..  •     27 

27.  Heating  Air  in  a  Flask      .        .      »,,..,  U        ..  .     28 

28.  Currents  of  Air  in  a  Refrigerator       .        .      .  ,*        ,   =  .     28 

29.  Ventilation  by  Window    .        .        .        .     - ,  ,        .  ..  .     29 

30.  Fireplace 30 

31.  Summer  Monsoon    .        .        .        .        ,     .  \    '   V  .    32 

xv 


xvi  LIST  OF  ILLUSTRATIONS 

FIGUKE  PAGE 

32.  Winter  Monsoon      .   '     .        .       ..        .        .        .        .     32 

33.  The  World's  Winds  .        .  A    ..    •/,,.      .        .        .        .33 

34.  Progress  of  a  Storm  Center       .        .- 33 

35.  Weather  Map   .         .         .        .        .        ....     34 

36.  Weather  Map  of  the  Following  Day         .        .        .        .35 

37.  Usual  Paths  of  " Highs"  and  " Lows"     ....     36 

38.  Tornado .        .        .37 

39.  Results  of  a  Severe  Windstorm         .        .        ...     38 

40.  Path  of  a  Hurricane .        ,        .        .'      .        .        .        .     39 

41.  Cumulus  Clouds       .    .     »"'     ;;  :     ,:  • . -';.  •     ..        .        .     40 

42.  Thunderstorm  .        ;        . 41 

43.  Touching  the  Surface  of  Water  with  a  Tuning  Fork.         .     45 

44.  One  of  the  Earliest  Talking  Machines       .        .        ;        .46 

45.  Phonograph      .-* .        .     47 

46.  Micro-photograph  of  Portion  of  a  Record         .        .        .     48 

47.  Phonograph  Record          .        .        .     '  v       .        ."•'     .     49 

48.  Telephone  Transmitter     <        .        .       -.        .        .    !     .     50 

49.  Human  Ear      .  '      .        .        .        .     '.''. :>-      .        .        .51 

50.  Oil  Fire    .        .        .        ^  .       ;.' '    ,'. ;;              .54 

51.  Lighted  Candle  under  Inverted  Glass  Jar         .        .        .     55 
52a.  Bunsen  Burner      ;    .       ..;      ;..        .        .        .        .        .     56 

526.  Gas  Stove  Burner     .        .        .        .        .        .                .    56 

53.  Movements  of  Piston  of  Gas  Engine         .        .        .   '     .     57 

54.  AMatch.        .     ''  ;v'      .        .        .        .        .        .        .     58 

55.  Rusting  of  Iron         .         .....        ....     60 

56.  Sectional  View  of  a  Hotbed      .        .        ,      ".        .        .     61 

57.  Factory  Wrecked  by  a  Dust  Explosion     .        .        .        .62 

58.  Available  Coal  Supply      .        .        .        .    *    .        .        .63 

59.  Coal  Fields  of  the  United  States     -.        .  r     ...     64 

60.  Fuel  Value  of  Some  Common  Foods         .'      -.    "     .        .     66 

61.  Flooded  Region        .        .        ;        .        ;        .        .        .68 

62.  Organs  of  an  Earthworm  .        .        .        .  '.'    .        •        .69 

63.  Stages  in  the  Life  History  of  a  Beetle       ....     71 

64.  Breathing  Organs  of  a  Fish 72 

65.  Results  of  a  Forest  Fire 74 

66.  Fire  Extinguisher 76 

67.  Fighting  a  Fire  with  Water       .        .        .        .     ;    .        .     77 

68.  A  Forest  Fire  Fighter        ....  .78 

69.  Forest  Ranger  on  Lookout  for  Signs  of  Forest  Fires          .    79 

70.  Preparation  of  Oxygen      .        ./      .        V-     -•        •        •    &1 


LIST  OF  ILLUSTRATIONS  xvii 

FIGURE  PAGE 

71.  Potato  Plant ;'.        1.      83 

72.  Coal  Bed       .  .     :    .  <•     .        .      i;V  '     .       ^.      86 

73.  Heating  Value  of  Some  Common  Fuels          <  .     -,if,      87 

74.  Oil  Wells  in  Oklahoma          . ';r  ^-   ".-.-,-  '. •••.•••!      88 

75.  A  Balanced  Aquarium           .         .         .  '  .',  •  7      89 

76.  Relation  of  Plants  and  Animals  in  a  Balanced  Aquarium     90 

77.  Colonies  of  Bacteria  and  Mold      ...  .        .      94 

78.  The  Four  Types  of  Bacteria  .        .      '  .        .  .        .      95 

79.  Wall  of  a  Refrigerator  .         .         ...  .         .98 

80.  Currents  of  Air  in  a  Refrigerator  .        .        .  .         .98 

81.  Iceless  Refrigerator        .         .         .         .         .  .         .       99 

82.  Framework  of  an  Iceless  Refrigerator    .        ;  .         .100 

83.  Ice  Plant ;        .     101 

84.  Storage  of  Butter  in  a  Refrigerating  Plant    .  ..        .     .102 

85.  Dead  Chestnut  Trees     .        .         .     ^/.'       .  .        .     109 

86.  A  Fresh  Air  Camp  in  California    .  .115 

87.  Results  of  Use  of  Diphtheria  Antitoxin  '•'.     118 

88.  Danger  of  Delay  in  Using  Antitoxin      .        .  .119 

89.  Roots  of  a  Bean  Plant  .        ....  .     124 

90.  Altocumulus  Clouds     .         .  V   129 

91.  Undulated  Alto-cumulus  Clouds   .         .         .  .  •    '   i     130 

92.  Cumulus  Clouds  over  Pacific  Ocean     ..        .  v     "•:     131 

93.  Rain  Gauge  .        .        •        •       ftSj      • 

94.  Snowflakes    . 

95.  Heavy  Fall  of  Snow  in  a  Pine  Forest    . 

96.  Average  Rainfall  of  the  United  States  .         .  .35 

97.  Landscape  in  an  Almost  Rainless  District  in  Arizona    .     136 

98.  Arizona  Desert  before  Irrigation    .  .     137 

99.  Arizona  Desert  after  Irrigation    •  .>  *        •     137 

100.  Roosevelt  Dam,  Arizona       .         *        •         •  .•,•-. 

101.  Map  Showing  Location  of  Irrigation  Projects  .        .     139 

102.  Russian  Salt  Fields        .         .       V       »    •    .  .'       .     141 

103.  Wet  and  Dry  Bulb  Thermometer  . 

104.  Transpiration  .  .        .        •• '.'••• 

105.  Upturned  Sugar  Maple .        U    .     .        «        .  •         •     146 

106.  Young  White  Cedars     .                         v   '     ;  .  -     .     147 

107.  Germinating  Wheat  Showing  Root  Hairs       .  .         -148 

108.  Root  Hairs    .        .         .        .                 .        .  ;  ;    '     .     148 

109.  A  Living  Tree  with  a  Hollow  Trunk     . 

110.  Lower  Epidermis  of  a  Leaf    .        .,                •  •        •     150 


xviii  LIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

111.  Train  Drawn  by  an  Electric  Locomotive     -,  ,     >;.',:     .     152 

112.  Waterfall,  McKenzie  River,  Oregon       ./     .        ;,      .     153 

113.  Diagram  of  a  Power  House    .         .         .         .         .   •     . .    154 

114.  Electric  High  Tension  Transmission  Line  -....-'    ; -.  J-      .     156 

115.  Water  Power  Station     ....  .157 

116.  Illustrating  Hydraulic  Pressure      .         .         ,        ...     .     157 

117.  Hydraulic  Press     .         ...         .         .         .         .         .     158 

118.  Source  of  Water  Supply  of  New  York  City  .        .;'.,     .     161 

119.  Kensico  Dam -'1J.     .     162 

120.  Height  to  Which  New  York  Water  Will  Rise        .  .•      .     162 

121.  Forest  Floor.         .         .         .         .       ...-,....        •    :     •     163 

122.  A  Stream  in  the  Catskill  Mountains     ...        .        .     164 

123.  Aerators         .         .         .         .         .         ,         .:        .'<      .     165 

124.  Diagram  of  a  City  Water  Supply  System      .       \  ...     166 

125.  Reservoir  and  Dam       .        .         .        .      ...;.     •„' .     .167 

126.  Limestone  Cave     .       ..;..-.        .,.       .        .     168 

127.  Water  Closet  Tank        .        .       . .        '.        .  ...••;        .     169 

128.  Trap  of  Waste  Water  Pipe    .      ...    s  .;-..-••  .    '     .     171 

129.  SepticTank.         .         .         .'.-,./     .        .         .-     .     172 

130.  Map  of  New  York  Harbor     .         .  :      .     -^        .        .     176 

131.  Coast  of  Eastern  United  States     .      :.        .        .-      .     177 

132.  Outline  of  South  America      ."->.        .        .        .        .     178 

133.  Outline  Map  of  England     -.        .        ..,..':,      .     179 

134.  Stratified  Rocks    .      ,.        .        .        .        .-.-..      .     180 

135.  Erosion  by  Small  Stream      .,        *.       .        .        .   ,     .     181 

136.  Flood  in  Wabash  River,  Indiana  .         ...         .         .182 

137.  Use  of  River  for  Transportation  of  Logs        .         .         .183 

138.  Use  of  Internal  Waterways  to  Transport  Farm  Products     184 

139.  Possibilities  of  Development  of  Internal  Waterways      .     185 

140.  United  States  Warship  Passing  through  Panama  Canal     187 

141.  Minot's  Ledge  Lighthouse     .         .         .     ,-.         .         .     188 

142.  High  Tide  in  a  Harbor  in  Nova  Scotia .         .         .         .192 

143.  Low  Tide  in  the  Same  Harbor      .        .        .        .        .192 

144.  Plumb  Line 194 

145.  Stable,  Unstable,  and  Neutral  Equilibrium  .         .         .     195 

146.  Relation  of  Moon  to  the  Tides      . '       .         .        .         .195 

147.  Action  of  Water  and  Mercury  in  Rotating  Glass  Globe     198 

148.  The  Two  Positions  of  the  Moon  When  High  Tide  Is 

Higher  than  Usual 200 

149.  The  Two  Positions  of  the  Moon  When  High  Tide  Is 

Not  as  High  as  Usual    .        .        .    ;     .        .        .     200 


LIST  OF  ILLUSTRATIONS    s  xix 


150.  Phases  of  the  Moon      .        .     -.        .        .   •    '.-'<      .    201 

151.  A  Total  Eclipse  of  the  Sun    .        .        .        .         .        .     202 

152.  Diagram  of  Our  Solar  System       .        .        .        .        .    203 

153.  Constellations  around  the  North  Star  ....     206 

154.  Evening  Sky  Map  for  January,  1921     .         .         .         .208 

155.  Heat  from  Sun,  Summer  and  Winter    .         .        .        .212 

156.  Path  of  Earth  around  the  Sun       .        .         .        .        .     212 

157.  Annual  Temperature  Curves 213 

158.  Lines  of  Latitude  and  Longitude 215 

159.  Standard  Time  Belts     J 216 

160.  Windmill 220 

161.  A  Negative '.        .         .221 

162.  Print  Made  from  Negative    .     -:•*        .        .        .        .222 

163.  Cold  Frame  .         .        .        .        ;        ....     224 

164.  Solar  Engine          ...         .         .         .  .224 

165.  Spring  Balance 229 

166.  Claw  Hammer 230 

167.  Crowbar .     231 

168.  Tongs 232 

169.  Scissors       v 232 

170.  Nutcracker    . 

171.  Arm  as  a  Lever     . 233 

172.  Well  Windlass 234 

173.  Part  of  a  Derrick 235 

174.  Placing  Heavy  Pipe  in  Position 236 

175.  Pulleys 237 

176.  Block  and  Tackle 238 

177.  Road  near  Colorado  Springs,  Colorado          .         .         .     239 

178.  Raising  a  Weight  by  Use  of  Inclined  Plane  .        .        .     239 

179.  Wedge  .         .         .        .        .        .      :  .        .       w        .     240 

180.  Screw .240 

181.  Demonstration  that  Screw  Is  an  Inclined  Plane    .         .     240 

182.  Jackscrew      .         .         .         .     •  v        .         .         .         .     240 

183.  "  Skidding  "Logs  on  Snow   .         .        .         .     "  ^  •      .     242 

184  a.  Roller  Bearings     .         .....         .        .         .         .     243 

1846.  Ball  Bearings         .         .         .    .    '.-        .         .         .         .243 

185(o,6,c,d).    Knots .245 

186.  Movements  of  Piston  in  a  Four-cycle  Engine    s    .         .     246 

187.  Sectional  View  of  an  Automobile 248 

188.  Grand  Central  Terminal,  New  York  City,  before  Elec- 

trification .  •       .252 


XX  LIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

189.  Grand  Central  Terminal,  New  York  City,  after  Elec- 

trification     ...        .        .         .        .        .  253 

190.  Direction  of  Current  through  an  Electric  Bell       .        .  254 

191.  A  Simple  Electromagnet        .         «:>.,-     •  .         r;,       .  255 

192.  Dynamo  Attached  to  an  Ambulance     .        ,        .        .  255 

193.  Arrangement  of  Iron  Filings  between  Poles  of  a  Magnet  256 

194.  Magnetic  Needle  .        .        .               ...        .         .  257 

195.  First  of  All  Electric  Batteries  Prepared  by  Volta,  A.  D. 

1800      .        .        .-     i  '. 257 

196.  Gravity  Cell        -,'•..     .    '     .        .      ;.   ,     .  -;     .  258 

197.  Daniel  Cell.        ...        ....     .        .         .         .  259 

198.  Dry  Cell        .         .         .         .        .        .        .     v  ..  ^     .  259 

199.  Structure  of  an  Induction  Coil      .         .         .         .    -     .  261 

200.  U.  S.  Army  Wireless  Operators  Receiving  Messages  from 

an  Airplane,  Tours,  France        .         .         .         .  262 

201.  A  Simple  Dynamo         .        .        ;        ...        .        .  263 

202.  Principle  of  Dynamo     .         .         ,        .         .-    a.v;"     .  263 

203.  A  Simple  Commutator 264 

204.  Use  of  Electric  Motor  in  Running  Sewing  Machine       .  264 

205.  Expc  i  imc  nt  1  Illustration  of  Principle  of  the  Motor      .  265 

206.  Si'ver  Plating    ....         .'      .         .       '.       ,. ',",     .  266 

207.  An  Electrotype     .         .        ...        .  .      .-     '.        .  267 

208.  E'ectric  Flatiron   .         ....       '.-      -      '•   '     •  268 

209.  Carbon  Filament  Lamp         .        .        -.        .        ,        .  269 

210.  Tungsten  Filament  Lamp      .         •        /.         .        ..         .  269 

211.  Amount   of   Light   Given   by   Different   Incandescent 

Lamps  .        .        ..       .        »        .»      ;  ...        i   •     .  269 

212.  Fuse      .         .        ,        .'                                                  .  270 

213.  Position  of  Carbons  in  an  Arc  Light     .        .        .     -:-..  270 

214.  Storage  Battery  Dissected  to  Show  Construction          .  272 

215.  Reflection  of  Light  from  a  Polished  and  a  Mirrored 

Surface          .     :  ,,        .         .         .        . . ;     .        :.  276 

216.  Reflection  of  Light  from  a  Smooth  Surface  .        .         .  277 

217.  Heliograph    .         ...         .         .  .278 

218.  Reflection  of  light  from  a  Slightly  Rough  and  a  Rough 

Surface 279 

219.  Relation  of  Intensity  of  lUumination  to  Distance  from 

Source  of  Light o,  -      .  279 

220.  Photometer  . 280 

221.  Gas  Meter  Reading  5700  Feet       .        .        .        ./       .  281 


LIST  OF  ILLUSTRATIONS  XXI 

FIGURE  PAGE! 

222.  Gas  Meter  Reading  68700  Feet  '-.'••    :  i"  ^     .^       ;'      .281 

223.  Face  of  a  Kilowatt  Hour  Meter    .      -';.  :      , ;  ~  4^     .     282 

224.  Relative  Costs  of  Different  Lights         .         .         .         .282 

225.  Comparative  Amounts  of  Light  Given  by  an  Open  Gas 

Flame  and  a  Gas  Mantle       .        .        .        .        .282 

226.  Cost  Per  Hour  of  Different  Gas  Lights          .        .        .283 

227.  Shaded  Light         .         .         .        .•'.'-.         .        .283 

228.  Lamp  Showing  Effect  of  Use  of  Shade  .     283 

229.  Reflection  of  Light  by  a  Polished  Metal  Reflector         .     284 

230.  Reflection  and  Transmission  of  Light   .  .     284 

231.  Breaking  Up  of  Light  in  Passing  through  a  Prism         .     287 

232.  Rays  of  Light  Passing  into  the  Eye       .  .289 

233.  A  Diagram  Showing  How  a  Light  Ray  May  Be  Bent  .     290 

234.  Bending  of  Rays  of  Light  by  Grooved  Glass  .  .     290 

235.  Change  of  Focus  of  Eye        .      y.  .291 

236.  Farsightedness  and  Its  Correction  .     292 

237.  Nearsightedness  and  Its  Correction       .        .  .      .        .     292 

238.  Magnifying  Glass •     295 

239.  A  Moving  Picture  Film  .....     296 

240.  Lines  Which  Deceive  the  Eye       .        .  .        .297 

241.  Thermos  Bottle 300 

242.  Fireless  Cooker     . 301 

243.  House  Heated  by  Hot  Air 304 

244.  House  Heated  by  Hot  Water         .        .        .        .        .305 

245.  Circulation  of  Water,  in  the  Radiator  and  around  the 

Cylinders  of  an  Automobile 306 

246.  Relative  Size  of  Soil  Particles       .      '.. .       ' .        .        .     309 

247.  Disintegration  of  Rock 310 

248.  Rugged  Mountains  Showing  the  Effect  of  Weathering  .     311 

249.  Weathered  Rock  at  Base  of  a  Cliff        .      •;",        .        .     312 

250.  Rock  Being  Split  by  the  Growth  of  a  Tree   .       f .   ;     .     313 

251.  Beech  Tree  Growing  on  Rocks      .        .        .        .        .     314 

252.  Water  Erosion       .         .         .     .    v:       .        .        v       .     315 

253.  Soil  Deposited  by  a  Glacier  .        .        .  H     .      -  ,-       .     315 

254.  Rock  Showing  Glacial  Scratches   .         .         i  -: '     .         .     316 

255.  Extent  of  Ice  Sheet  during  Glacial  Period     .        v       .     317 

256.  A  Glacier 'V       ,     :  V        .     318 

257.  Front  of  a  Glacier,  Mt.  Rainier  National  Park    .        .     319 

258.  Formation  of  Humus    .  '      .        ....         .319 

259.  Vacant  Lot  Garden  .        .        .       V      .322 


xxii  tIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

260.  Absorption  of  Water  by  Soils        .        .     K  ..      ....  .     323 

261.  Lumbermen  at  Work    ....        ,.  .      .  .     330 

262.  Composition  of  Bread  and  Cereal  Foods        .        .  •  .332 

263.  Composition  of  Some  Common  Vegetables    .        .  .     333 

264.  Composition  of  Fish  and  Oysters  .        .        ,.,  .     .  .     334 

265.  Composition  of  Eggs  and  Cheese  ....  .     335 

266.  Composition  of  Various  Grains  Used  for  Food      .  .     336 

267.  Cross  and  Longitudinal  Sections  of  a  Young  Root  .     344 

268.  Food  Canal  (Alimentary  Canal)  of  Man       .        ....  .346 

269.  Organs  of  Circulation  of  Man       ,.     .  .        .      -  •.  ;  .     347 

270.  Seeds  of  Bean  and  Pea          .—  .   .     .    _;..        .  .     350 

271.  Sprouting  Corn  Grain  .        .    r     .        v        .        •  •     351 

272.  Pear,  from  Bud  to  Fruit  and  Seed         .         .        .  .     352 

273.  Growth  of  Pollen  Tubes  Down  through  the  Style  .     354 

274.  Pollen  Tube  Entering  Ovule          .        .        ...     355 

275.  Pistillate  Flowers  of  Corn     .        .        .       ..       . ...  .     356 

276.  Corn  Tassel  Made  Up  of  Staminate  Flowers         .  .     357 

277.  Staminate  Flowers  of  Chestnut     .        ...  .     358 

278.  Flowers  of  Oak     ...        .        .        .        .-     ."  .     358 

279.  Flowers  of  Horsechestnut      .        .        .        .        ..    ,  .     359 

280.  Cherry  Blossoms  .        .                 .      '...- ...  .     360 

281.  Variation       .        .        .        ...       .        .•<  •     .        .  ;,  .     364 

282.  Tongue  Grafting  .        .        .  ,     .       ,.   (j    .  ft    .* ,,>  .     365 

283.  Cleft  Grafting       .         .     -, ,, .  ;:    .     • '....  :     .  --*...  .     366 

284.  Budding,  a  Form  of  Grafting       Vv    .-       ,\-     ,-  .     366 

285.  Life  History  of  Gypsy  Moth         .        .        .-      .  .     369 

286.  Potato  Beetle        .        .      .'',.•   .-.    . ;      .        .        .  .     370 

287.  Peach -Tree  Borer          .        .        ..;    ...  .370 

288.  Group  of  Dying  Locust  Trees       .        .        .:        .  .371 

289.  Worm  in  Apple,  Larva  of  Codling  Moth       .        .  .371 

290.  Scale  Insects  on  a  Fern  Leaf         .        .   •  .  .  ;<     .  .     372 

291.  Tent  Caterpillars  .         .        ^:      v.      .>      >  .-.'     .  •     373 

292.  A  Modern  Spraying  Outfit    .        ..        v  .      .        .  .     374 

293.  A  Beneficial  Beetle        .       =.;..,;,      .        .  .375 

294.  Ladybird  Beetle 376 

295.  Ladybird  Beetle  Feeding  on  Scale  Insects     .        .  .377 

296.  Toads  Eating  Caterpillars 378 


ACKNOWLEDGMENTS  OF 
ILLUSTRATIONS 


Chicago,  Milwaukee,  and  St.  Paul  R.  R.,  No.  113. 

Columbia  Graphophone  Company,  No.  44,  45. 

Ford  Motor  Company,  No.  214,  245. 

Forest  Service,  U.  S.  Dept.  Agriculture,  No.  39,  61,  65,  68,  69,  85, 

86,  92,  95,  97,  105,  106,  109,  112,  121,  125,  134,  135,  137,  177, 

183,  248,  250,  251,  252,  253. 

General  Electric  Company,  No.  26,  111,  115,  188,  189,  204. 
Grand  Trunk  R.  R.,  No.  256. 
Harvey  Conard,  Hollis,  New  York,  No.  239. 
John  Reiss,  New  York  City,  No.  21. 
Leon  Barritt,  Brooklyn,  New  York,  No.  154. 
New  York  Board  of  Health,  No.  87,  88. 
New  York  Zoological  Society,  No.  475. 
National  Lamp  Works,  General  Electric  Company,  No.  215,  216, 

217,  218,  227,  228,  229,  230,  234. 
Packard  Motor  Company,  No.  1,  187. 
Pacific  Northwest  Tourist  Association,  No.  257. 
Pennsylvania  Lines,  No.  136. 

Signal  Corps,  American  Expeditionary  Force,  No.  11,  192,  200. 
Thomas  Edison,  Inc.,  No.  46,  47. 
U.  S.  Bureau  of  Chemistry,  No.  57,  67. 
U.  S.  Bureau  of  Entomology,  No.  63,  287,  288,  293,  295,  296. 
U.  S.  Bureau  of  Standards,  No.  219,  221,  222,  223,  224,  225,  226. 
U.  S.  Dept.  of  Agriculture,  No.  81,  82,  84,  263,  264,  265,  266,  267. 
U.  S.  Geological  Survey,  No.  50,  58,  59,  72,  74. 
U.  S.  Naval  Observatory,  No.  151. 
U.  S.  Reclamation  Service,  No.  98,  99,  100,  101,  114. 
U.  S.  Weather  Bureau,  No.  6,  8,  34,  35,  36,  37,  38,  41,  90,  91,  93, 

94,  103. 

U.  S.  Navy,  No.  42. 

Wcston  Electrical  Instrument  Company,  No.  193,  195,  201,  205. 

xxiii 


GENERAL   SCIENCE 

UNIT  I 

RELATION   OF  AIR  TO  EVERYDAY  ACTIVITIES 

PROJECT   I 
IMPORTANCE   OF   THE   WEIGHT   OF  AIR 

FOR  many  centuries  men  who  experimented  with  the  prob- 
lem of  keeping  a  body  heavier  than  air  moving  through  it 
as  a  bird  flies  were  the  objects  of  ridicule  and  derision.  Only 
so  short  a  time  ago  as  1905,  the  first  successful  flying  machine 
was  invented  by  Wilbur  and  Orville  Wright  of  Dayton, 
Ohio. 

Now,  after  invaluable  service  in  the  Great  War,  the  air- 
plane in  a  highly  perfected  stage  has  crossed  the  Atlantic 
Ocean.  It  has  crossed  our  continent,  a  distance  of  3000 
miles,  in  25  hours  of  actual  flying  time.  One  of  man's 
greatest  ambitions  has  become  a  reality,  and  without  doubt 
the  future  holds  further  achievement  in  the  development  of 
the  airplane  as  wonderful  as  that  of  the  last  few  years. 

Problem  1.  How  an  airplane  remains  in  the  air.  —  The 
study  of  the  kite  may  help  us  to  understand  the  airplane. 
Is  it  possible  to  fly  a  kite  on  a  day  when  there  is  no  wind? 
In  starting  to  fly  a  kite,  does  a  boy  run  with  or  against  the 
wind?  Is  running  necessary  to  start  the  kite  on  a  day 
when  a  strong  wind  is  blowing  ?  What  happens  if  the  string 

1 


IMPORTANCE  OF   THE  WEIGHT  OF  AIR 


breaks?  What  is  the  purpose  of  the  tail  of  the  kite?  As 
a  result  of  a  consideration  of  these  questions,  it  will  be  un- 
derstood that  a  plane  or  flat  surface,  if  held  at  the  proper 
angle,  is  kept  up  by  the  force  exerted  by  the  air  in  motion. 
That  air  in  motion  has  great  force,  is  well  known  to  us. 
The  destruction  caused  by  a  severe  wind  is  sufficient  proof 


FIGURE  2.  —  AIRPLANE  IN  AIR. 

of  this.  We  are  also  familiar  with  the  fact  that  even  when 
there  is  no  movement  of  the  air,  the  same  force  is  exerted  if 
an  object  is  passing  rapidly  through  the  air.  A  ride  on  the 
front  seat  of  a  street  car  or  in  a  rapidly  moving  automobile 
convinces  us  of  the  force  which  may  be  considered  to  be 
exerted  either  by  the  moving  body  or  by  the  air. 

The  airplane  with  its  light,  high  power    engine  is  able 
by  means  of  its  propellers  to  attain  great  speed  through  the 


GENERAL  SCIENCE 


air.  The  planes  may  be  so  controlled  that  they  present  the 
proper  angle  to  the  air.  .  The  same  force  is  exerted  if  the 
machine  is  moving  75  miles  per  hour,  as  if  the  machine  were 


FIGURE  3.  —  UNITED  STATES  AIRPLANE. 

Photographed  on  the  flying  field  at  Tours,  France.  Explain  the  appear- 
ance of  the  propeller  and  the  dust  cloud  behind  and  to  the  left  of  the 
machine.  Note  the  slant  of  the  planes. 

stationary  and  the  air  were  moving  75  miles  per  hour.  It 
will  thus  be  seen  that  the  airplane  remains  in  the  air  for  the 
same  reason  that  a  kite  remains  in  the  air.1 

Problem  2.  Has  air  weight?  —  As  the  propeller  of  the 
airplane  drives  the  machine  through  the  air  very  much  as 
the  propeller  of  a  boat  drives  it  through  the  water,  air 
seems  to  be  a  substance,  just  as  water  is.  If  this  is  true, 
it  should  have  weight.  Weight  is  the  measure  of  the  pull 
of  the  earth  (gravity)  upon  particles  composing  various 

1  Many  pupils  will  want  to  make  model  airplanes.  At  the  end  of 
the  chapter  references  are  given  which  will  provide  directions  as  to  the 
details  of  their  construction. 


IMPORTANCE  OF   THE   WEIGHT  OF  AIR 


materials.     The    weight    of    a    book    is    the    measure    of 
the  pull  of  the  earth  upon  the  book.     If  we  drop  it,  it  falls 
or  is  pulled  toward  the 
center  of  the  earth.    How 
may  we  discover  that  air 
has  weight  ?    The  follow- 
ing experiment  has  been 
tried  many  times. 


FIGURE  4. 


Experiment. — Weigh  care- 
fully a  strong  flask ;  then  by 
means  of  an  air  pump  remove 
the  air  from  it  and  weigh  it 
again.  What  is  the  result? 
That  air  has  weight,  may 
also  be  shown  by  blowing  up 

a  basket  ball  or  football  until  it  is  full  and  then  weighing  it  (Figure  4), 
and  after  allowing  the  air  to  escape,  weighing  it  again  (Figure  5). 

Careful  weighing  has  shown  that  one  cubic  foot  of  dry  air 
at  sea  level  and  at  the  freezing  temperature  (of  water)  weighs 

about  one  thirteenth  of 
a  pound.  Calculate  ap- 
proximately the  weight 
of  the  air  in  the  school- 
room ;  in  your  bedroom, 
etc. 

Problem  3.  Does  air 
press  upon  things?  —  If 
air  has  weight,  it  should 
exert  pressure  upon 

everything;    because  the  atmosphere  extends  many  miles 

above  the  earth's  surface. 


FIGURE  5. 


6 


GENERAL  SCIENCE 


Experiment.  —  Into  a  tin  can  which  has  a  small  opening,  put  a  few 
spoonfuls  of  water.  Heat  the  can  until  sufficient  steam  is  formed  to 
drive  out  the  air.  Plug  the  opening  in  the  can  with  an  airtight  stopper. 

As  the  can  cools,  the  steam  changes  back 
to  water  and  the  space  within  the  can 
contains  neither  steam  nor  air  and  is 
called  a  vacuum. 

What  happens  to  the  can  ?  Explain. 
Use  a  wide-mouthed  bottle  instead  of 
the  can  and  in  place  of  the  stopper  tie 
a  piece  of  paper  or  still  better  a  piece  of 
sheet  rubber  over  the  opening.  Result  ? 
Conclusion  ? 

Problem  4.  How  air  pressure 
may  be  measured.  —  The  amount 
of  this  pressure,  which  of  course 
will  also  be  the  measure  of  the 
weight  of  the  air  over  a  certain 
space,  may  be  found  by  repeating 
the  experiment  of  Torricelli,  a 
pupil  of  Galileo,  made  in  1643. 
This  was  the  first  measurement 
made  of  air  pressure. 

Experiment.  —  Fill  with  mercury  a 
glass  tube  about  three  feet  long  and 
closed  at  one  end.  Closing  the  open  end 
with  the  finger  to  prevent  the  escape  of 
the  mercury,  invert  the  tube  and  place 
the  open  end  below  the  surface  of  mer- 
cury in  a  dish.  Now  withdraw  the  finger 
and  note  the  result  (Figure  6).  What 
keeps  the  mercury  in  the  tube  above 
the  level  of  the  mercury  in  the  dish? 

If  the  tube  has  a  cross  section  of  one  square  inch,  the 
weight  of  the  mercury  held  above  the  level  of  the  mercury 


FIGURE  6.  —  SIMPLE  BAROME- 
TER. 

Why  must  one  end  of  the 
tube  be  closed?  Where  does 
the  air  press  ?  Why  does  the 
mercury  not  reach  the  top  of 
the  tube  ?  Scale  is  in  inches. 


IMPORTANCE  OF   THE  WEIGHT  OF  AIR 

in  the  dish  will  be  about  fifteen  pounds. 
Therefore  it  may  be  stated  that  air  exerts  a 
pressure  of  about  fifteen  pounds  per  square 
inch. 

The  apparatus  used  in  this  experiment  con- 
stitutes the  essentials  of  a  mercury  barometer 
(Figure  7).  Since  weather  changes  are  ac- 
companied and  frequently  preceded  by  changes 
in  air  pressure,  the  practical  value  of  the 
barometer  may  be  understood. 

Problem  5.  Why  water  is  not  used  in  mak- 
ing barometers.  —  From  the  last  experiment 
we  learn  that  the  pressure  of  the  air  will  hold 
up  a  column  of  mercury  about  30  inches  in 
height.  Would  a  longer  or  shorter  column  of 
a  lighter  liquid  be  held  up?  Explain.  Evi- 
dently, therefore,  in  selecting  a  liquid  to  be 
used  in  a  barometer,  its  weight  must  be  con- 
sidered. 

Experiment.  —  Into  each  of  two  beaker  glasses  put 
respectively  equal  volumes  of  mercury  and  water. 
Lift  the  glasses.  Which  is  the  heavier?  Put  the 
beaker  glasses  containing  the  mercury  and  water  on 
the  opposite  pans  of  a  balance  and  by  the  use  of 
weights  find  out  how  much  heavier  one  substance  is 
than  the  other.  What  is  the  Jesuit  ? 

FIGURE  7.  —  MERCURIAL  BAROMETER. 

The  height  of  the  mercury  column  is  measured  in 
centimeters,  c,  surface  of  mercury  upon  which  air  is  pressing,  a,  screw 
by  which  the  mercury  in  the  mercury  cup  is  adjusted  so  that  the  surface  (c) 
is  at  the  zero  point  of  the  barometer  tube,  d,  thermometer,  e,  screw  for 
adjustment  of  a  scale  (vernier)  by  which  the  height  of  the  mercury  may  be 
read  more  accurately.  /,  scale  at  top  of  mercury  column. 


8 


GENERAL  SCIENCE 


If  mercury  is  thirteen  and  one-half  times  heavier  than 
water  calculate  the  height  of  a  column  of  water  that  may  be 
held  up  by  the  pressure  of  the  air.  Such  a  barometer  was  con- 
structed by  Otto  von  Guericke,  the  inventor  of  the  air  pump. 


FIGURE  8.  —  ANEROID  BAROMETER. 

The  upper  portion  of  the  tube  to  the  extent  of  about  six  feet 
was  of  glass.  Floating  on  the  top  of  the  liquid,  the  inventor 
had  introduced  a  small  figure  of  a  man  which  with  the  rising 
of  the  column  in  fair  weather  presented  itself  to  view ;  but 
with  the  approach  of  foul  weather  retreated  out  of  sight. 


IMPORTANCE  OF  THE  WEIGHT  OF  AIR 


9 


Ptin&r 


C/ia/f\ 


Problem  6.  How  an  aviator  knows  how  high  he  is.  — 
If  a  barometer  is  carried  up  a  mountain  the  mercury  column 
drops  about  0.1  of  an  inch  for  every  90  feet  of  elevation. 
Explain  why  this  is  so.  Explain  how  an  aviator  is  able  to 
determine  his  height  above  the  earth.  Why  is  a  mercury 
barometer  unfitted  for  use  in  an  airplane  ? 

Can  you  suggest  a  method  of  making  a  barometer  which 
will  not  have  the  objectional  features  of  the  mercury  barom- 
eter? Reference  to  the  experiment  in  Problem  3  may  help 
you.  Suppose  some  of  the 
air  is  removed  from  a  me- 
tallic box,  having  sides 
that  go  in  or  out  as  the 
pressure  on  it  changes. 
What  will  happen  to  the 
sides  when  this  box  is 
carried  up  in  an  airplane  ? 
When  it  is  carried  back 
to  the  earth  again  ? 

The  aneroid  barometer 
is  made  according  to  this  plan.  In  its  simplest  form  it  is  a 
metal  box  from  which  a  large  part  of  the  air  has  been  re- 
moved. The  cover  will  bend  slightly  with  changes  of  pressure 
of  the  atmosphere.  By  a  series  of  levers  the  extent  of 
movements  of  the  cover  of  the  box  is  multiplied  and  repre- 
sented by  a  pointer  on  a  dial. 

Problem  7.  Why  air  pressure  does  not  prevent  us  from 
lifting  objects.  —  Calculate  the  weight  of  air  resting  on  a 
book  six  by  ten  inches.  You  know,  however,  that  the  book 
can  be  lifted  as  though  there  were  no  weight  on  it.  The  follow- 
ing experiment  may  help  you  to  understand  how  this  can  be. 


Vacuum  bop 


FIGURE  9.  —  DIAGRAM  OF  AN  ANEROID 
BAROMETER. 


10 


GENERAL  SCIENCE 


Experiment.  —  Completely  fill  a  glass  with  water  and  cover  the  top 
of  it  with  a  piece  of  cardboard,  making  certain  that  the  cardboard  is 
everywhere  in  close  contact  with  the  edge  of 
the  glass.  Invert  the  glass  (Figure  10).  What 
happens  ?  Why  ?  Hold  the  glass  in  different 
positions.  Result  ?  Conclusion  ? 


FIGURE  10. 


Problem  8.  Why  a  balloon  or  a 
dirigible  remains  in  the  air.  —  Why  do 
you  think  that  the  explanation  given 
for  the  airplane  remaining  in  the  air  will 
not  account  for  the  buoyancy  of  a  bal- 
loon? Since  we  have  learned  that  air 

has  weight  we  may  compare  the  floating  of  objects  in  air 

with  the  floating  of  objects  in  water.     You  know  from 

experience  that  objects  like 

iron   and    stones,     that   are 

heavier  than  water,   will  sink 

while  cork  and   wood,  which 

are  lighter    than  water,  will 

float. 

The  same  is  true  of  things 

in  the  air.     Cork   and  wood 

and  most  things  we  know  of 

are  heavier  than  air  and  will 

not  float  in  it.     A  balloon, 

however,  is    lighter  than  air 

and  therefore  will  float  in  it. 


We  know  that  air  pressure 
is  exerted  in  all  directions. 
The  air  under  the  balloon, 
therefore,  is  pushing  it  up- 
ward and  the  air  above  it, 


t 


FIGURE  11.  —  FRENCH  WAR  BALLOON. 

It  is  making  an  ascent  at  St.  Nazaire, 
France. 


IMPORTANCE  OF  THE  WEIGHT  OF  AIR  11 

is  pushing  it  downward.     If  the  balloon  weighs  the  same  as 
air  it  will  not  be  pushed  either  upward  or  downward.     If, 


FIGURE  12. 


however,  the  balloon  weighs  more  than  an  equal  volume  of 
air,  will  the  downward  or  upward  pressure  be  greater? 
Explain.  If  the  balloon  weighs  less  than  the  air  that  it 


FIGURE  13. 


displaces,  which  pressure  will  be  the  greater?  Explain. 
Explain  why  a  balloon  does  not  continue  to  go  up  until  it 
reaches  the  top  of  the  atmosphere. 


12 


GENERAL  SCIENCE 


Balloons  and  dirigibles  must  be  filled  with  a  gas  much 
lighter  than  air.  Hydrogen  gas,  which  is  about  14|  times 
lighter  than  air,  has  been  the  gas  generally  used.  The  use 


FIGURE  14. 
Note  that  the  can  at  the  right  has  two  holes  in  its  top. 

of  hydrogen  for  filling  balloons  may  be  shown  by  making 
soap  bubbles  with  it. 

Experiment.  —  Make  hydrogen  by  setting  up  the  apparatus  shown 
in  Figure  12  and  pouring  hydrochloric  acid  through  the  tube  with  the 
enlarged  top  (thistle  tube)  over  the  pieces  of  zinc  in  the  flask.     By 
means  of  a  rubber  tube  attach  the  stem  of 
a  clay  pipe  to  the  tube  which  carries  the  gas 
from  the  flask.     Dip  the  bowl  of  the  pipe 
into  soapsuds.     Shake  off  the  bubbles  into 
the  air  as  they  are  formed    and  note  their 
behavior.     Touch   a   bubble  with  a  match 
and  observe  what  happens. 


A  new  gas  (helium)  which  is  found 
in  considerable  quantities  mixed  with 
the  gas  of  some  natural  gas  wells  is 
now    being     used.    It    is    somewhat 
heavier  than  hydrogen  although  much 
FIGURE  15.  —  RELATIVE   lighter  than  air.    The  great  advantage 
^  its  use  is  that  it  will  not  burn, 
EXPIRATION.  whereas  hydrogen  does. 


IMPORTANCE  OF   THE  WEIGHT  OF  AIR 


13 


EXERCISES 
Explain  tile  following : 

(1)  How   ink  may  be  drawn  up 
into  a  medicine  dropper  such  as  is  used 
in  filling  a  fountain  pen  (Figure  13). 

(2)  How  lemonade  may  be  sucked 
through  a  straw. 

(3)  Why  olive  oil  or  any  other  liquid 
can  readily  be  poured  from  a  small  open- 
ing in  a  can  if  there  is  another  opening 
above  the  liquid,  but  will   not  flow 
evenly  if  this  opening  is  closed  (Fig- 
ure 14). 

(4)  Why  a  fountain  pen  frequently 
leaks  when  it  is  nearly  empty. 

(5)  Why  the  raising  of  the  ribs 
and  lowering  of  the  diaphragm  of  the 
body  causes  air  to  flow  into  the  lungs 
(Figure  15). 

(6)  Why  two  pieces  of  wet  glass 
stick  .together. 

(7)  The  action  of  non-skid  auto- 
mobile tires  (Figure  16). 

(8)  Theabil- 


FIGURE  17. —  SOLE  OF 
BASKET  BALL  SLIPPER. 


FIGURE  16.  —  NON-SKID  AUTO- 
ity  of  basketball  MOBILE  TlRE' 

players  to  keep  from  slipping  on  the  smooth  floor 
of  a  gymnasium  (Figure  17). 

(9)  Action  of  the  ordinary  suction  pump 
(Figure  18).  How  high  will  such  a  pump  lift 
water  ? 

(10)  How  air  pressure  may  help  in  removing 
liquids  from  casks  or  large  bottles  (siphoning). 
(Figure  19.) 

(11)  Action  of  a  vacuum  cleaner.     Why  is 
its  use  advisable? 

(12)  Why  one's  hat  is  apt  to  be  carried  off  as 
a  swiftly  moving  train  passes. 


14  GENERAL   SCIENCE 

(13)  The  action  of  a  self-filling  fountain  pen. 

(14)  Difficulty  of  drinking  from  a  small-mouthed  bottje. 


FIGURE  18.  —  SUCTION  PUMP. 

V,  V  valves ;  P,  piston ;  5,  pump  stem ;  W,  water  of  well.  What 
causes  V  to  open  as  piston  moves  upward  ?  What  will  be  the  position 
of  valves  as  piston  is  pushed  downwards  ? 

(15)  Sucking  of  blood  by  a  mosquito." 

(16)  Noise  caused  by  removing  a  thimble  from  a  wet  finger. 


FIGURE  19.  —  SIPHONING  LIQUID  FROM  A  BARREL. 

The  tube  fits  loosely  in  the  opening  at  the  top  of  the  barrel.  Why  is  this 
necessary  ?  Why  cannot  this  barrel  be  completely  emptied  by  the  tube  as  it 
is  ?  How  can  this  tube  be  changed  so  that  the  barrel  may  be  emptied  with  it  ? 

(17)  Difficulty  of  pouring  a  liquid  through  a  funnel  which  fits  tightly 
into  the  mouth  of  a  jug  or  bottle.     How  may  the  liquid  be  made  to  flow 
rapidly  ? 

(18)  Why  the  body  is  not  crushed  by  the  pressure  of  the  air. 


WEIGHT  OF  AIR  15 

SUGGESTED  INDIVIDUAL  PROJECTS1 

1.  Make  a  kite  and  demonstrate  by  diagrams  how  it  is  able  to  fly. 

2.  Make  an  air-glider  and  explain  how  it  acts. 

3.  Make  a  model  airplane  that  will  fly  and  demonstrate  its  action 
to  the  class. 

4.  Construct  a  homemade    mercury  barometer  and  record   for  a 
period  of  time  the  changes  in  air  pressure.     At  the  same  time  make  a 
record  of  the  condition  of  the  weather  and  determine  if  there  seems  to 
be  any  connection  between  changes  in  air  pressure  and  the  weather. 

5.  Construct  and  demonstrate  a  suction  pump. 

6.  Demonstrate  that  air  is  heavier  than  hydrogen  gas  and  is  lighter 
than  carbon  dioxide  gas. 

7.  Construct  an  apparatus  to  illustrate  the  expansion  and  con- 
traction of  the  lungs  in  breathing. 

8.  Demonstrate  the  structure  and  action  of  a  self-filling  fountain 
pen. 

9.  Demonstrate  the  structure  and  action  of  a  vacuum  cleaner. 
10.    Construct  a  siphon  and  demonstrate  its  use.     Discuss  various 

applications  that  may  be  made  of  the  siphon. 

REPORTS 

1.  First  successful  attempts  to  cross  the  Atlantic  Ocean  in  an  air- 
plane. 

2.  Early  attempts  to  develop  the  airplane. 

3.  The  use  of  the  airplane  in  the  Great  War. 

4.  Commercial  possibilities  of  the  airplane. 

REFERENCES  FOR  PROJECT  I 

1.  Aircraft  Today,  Chas.  Turner.     J.  B.  Lippincott  Co. 

2.  How  to  Fly,  F.  A.  Collins.     D.  Appleton  &  Co. 

3.  The  Air  Men,  F.  A.  Collins.     Century  Co. 


1  As  explained  in  the  Preface,  not  all  the  Individual  Projects  are  to  be 
required  of  every  student.  Some  are  for  girls,  some  for  boys ;  some  for 
city  pupils,  some  for  country  students ;  some  are  so  simple  that  nearly 
anyone  can  perform  them  easily,  while  some,  like  Project  3  above,  will 
appeal  only  to  those  who  have  a  decided  mechanical  talent. 


16  GENERAL  SCIENCE 

4.  Boys' Book  of  Airships,  H.  Delacombe.     Frederick  A.  Stokes  Co. 

5.  How  It  Flies,  Richard  Ferris.     Thomas  Nelson  &  Sons. 

6.  The  Story  of  the  Airplane,  C.  Graham-White.     Small,  Maynard 
&Co. 

7.  Boys'  Book  of  Model  Airplanes,  Vols.  I  and  II,  F.  A.  'Collins. 
Century  Co. 

8.  Aviation  Book,  Curtis.     F.  A.  Stokes. 

9.  Harper's  Book  on  Aircraft,  Verrill.     Harper  &  Bros. 

10.  Boys'  Book  of  Inventions,  Baker.     Doubleday,  Page  &  Co. 

11.  Flying  Machines,  etc.,  The  American  Boy's  Handy  Book,  Beard. 
Charles  Scribner's  Sons. 

12.  War  Kites,  Field  and  Forest  Handy  Book,  Beard.     Charles 
Scribner's  Sons. 

13.  Handicraft  for  Handy  Boys,  Hall.     Lothrop,  Lee  &  Shepard. 

14.  Historic  Inventions,  Holland.     Geo.  W.  Jacobs  Company. 

15.  Harper's  Outdoor  Book  for  Boys.     Harper  &  Bros. 

16.  The  Outdoor  Handy  Book,  Beard.     Charles  Scribner's  Sons. 

17.  Practical  Things  with  Simple  Tools,  M.  Goldsmith.     Sully  & 
Kleinteich. 

18.  Careers  of  Danger  and  Daring,  Cleveland  Moffet.     Century  Co. 
(Divers,  Balloonists,  Bridge  Builders,  etc.) 

19.  The  Barometer  as  the  Footrule  of  the  Air.     Taylor  Instrument 
Co.,  Rochester,  N.  Y.,  10  cents. 

20.  The  Thermometer  and  Its  Family  Tree.     Taylor  Instrument 
Co.,  10  cents. 

21.  The  Story  of  Great  Inventions.     Harper  &  Bros. 

22.  Modern  Triumphs,  E.  M.  Tappan,  Editor.    Houghton  Mifflin 
Co. 

23.  Harper's  Machinery  Book  for  Boys.    Harper  &  Bros. 


PROJECT  II 
HOW  WE  USE   COMPRESSED  AIR 

THE  fact  that  we  not  only  make  use  of  air  pressure 
but  also  of  compressed  air  is  familiar  to  us  all.  Automo- 
biles weighing  several  thousands  of  pounds  are  held  up  by 
compressed  air.  The  construction  of  bridge  foundations 
and  tunnels  under  the  beds  of  rivers  is  made  possible  by 
it.  Moving  trains  weighing  hundreds  of  tons  may  be 
quickly  brought  to  a  stop  by  the  air  brake.  Drills,  rivet- 
ing machines,  and  many  other  appliances  are  operated  by 
compressed  air.  How  such  a  substance  as  air  can  do  all 
these  things  opens  up  for  us  many  problems. 

Problem  1.  How  air  pressure  is  used  in  building  founda- 
tions and  subways.  — What  is  an  air  bubble?  Can  air  and 
water  occupy  the  same  space  at  the  same  time? 

Experiment.  —  To  find  out  if  air  and  water  can  occupy  the  same 
space  at  the  same  time,  push  down  into  a  vessel  of  water  an  inverted 
drinking  glass  (Figure  20).  What  is  the  result?  It  is  evident  that 
the  pressure  of  the  air  within  the  glass  is 
sufficient  to  prevent  the  entrance  of  the 
water  into  the  glass. 

This  pressure   is   equal  to  the 
weight    of    the   column  of   water 

above  the  level  of  the  water  which 

.     .  .         „      .          .  i,i_  FIGURE  20. 

is    inside  or    the   glass    plus   tne 

ordinary  atmospheric  pressure   (how  much?)   on  the  sur- 
face of  the  water.     As  the  glass  is  pushed  downward  will 

17 


18 


GENERAL  SCIENCE 


any  change  occur  in  the  amoun^  of  pressure  exerted  by  the 
contained  air?  At  what  depth  in  the  water  will  the  air 
exert  a  pressure  equal  to  two  atmospheres?  At  this  point 
the  volume  of  the  air  will  be  one  half  of  its  original  volume, 
illustrating  a  law  of  every  true  gas,  that  the  volume  varies 


5TCAM  BABGE  fOU 

I  HOSTING.  FUPNISMING 
COMPPE5SEDAIB,  &, 
ELECTBIUTY 


FIGURE  21.  —  CAISSON. 

If  the  pressure  of  the  air  in  the  caisson  is  about  30  pounds  per  square 
inch,  how  far  from  the  surface  of  the  water  is  the  bottom  of  the  excavation  ? 
What  would  happen  if  the  doors  at  the  top  should  be  left  open  ?  Why  ? 

inversely  as  the  pressure  exerted  upon  it.     This  law  is  known 
as  Boyle's  law. 

Caissons  used  in  building  foundations  under  water  are 
large  metal  cylinders  open  at  the  bottom,  into  which  air 
is  pumped  until  it  exerts  sufficient  pressure  to  prevent  the 
entrance  of  water  (Figure  21).  Air  under  pressure  was  used 


HOW    WE    USE   COMPRESSED   AIR  19 

to  keep  out  the  water  during  the  construction  of  the  tunnels 
under  the  East  and  North  rivers  at  New  York  City. 

Great  care  must  be  taken  by  men  passing  from  the  com- 
pressed air  chambers  to  the  outer  air.  If  this  is  done  too 
quickly,  gases  which  are  dissolved  in  the  blood  form  small 
bubbles  which  prevent  the  blood  from  passing  through 
capillaries  (very  small  blood  vessels),  causing  an  acute 
disease,  the  "  bends."  To  prevent  this,  a  man  instead  of 
passing  directly  into  the  outer  air  goes  through  several 
rooms  of  graduated  pressures,  remaining  in  each  room  a 
sufficient  length  of  time  to  permit  the  body  to  accommodate 
itself  to  the  changed  pressure. 

Problem  2.  How  compressed  air  is  used  in  automobile 
tires.  —  We  all  know  that  bicycle  tires  and  most  automo- 
bile tires  are  filled  with  air.  At  first  thought  it  seems  strange 
that  a  substance  like  air  can  hold  up  the  great  weight  of  a 
heavy  automobile.  Naturally  we  ask  how  this  air  is  dif- 
ferent from  the  air  around  us. 

What  happens  if  a  nail  punctures  the  tire?  Sometimes 
when  the  outer  covering  of  the  tire  becomes  badly  worn  a 
"  blow-out  "  occurs  with  a  noise  like  an  explosion,  tearing  a 
hole  in  the  tire.  What  does  this  indicate  to  you  concern- 
ing the  condition  of  the  air  within  the  tire  ? 

It  is  evident  that  the  compressed  air  in  the  tire  is  able  to 
hold  up  the  weight  of  the  automobile  amounting  to  several 
thousand  pounds,  just  as  the  compressed  air  in  the  diving 
bell  resists  the  pressure  of  the  water. 

If  you  have  ever  ridden  in  a  solid-tired  automobile 
and  then  in  one  having  pneumatic  or  air-filled  tires,  you 
have  noticed  that  in  the  latter  case  the  jars  caused  by 
the  roughness  of  the  road  were  not  felt  as  much.  This 


20  GENERAL   SCIENCE 

observation  shows  that  the  compressed  air  in  the  tire  acts 
like  a  spring.  The  following  simple  experiment  will  show 
this  effect  of  compressed  air. 

Experiment.  —  Bounce  together  on  the  floor  a  new,  perfect  tennis 
ball  and  a  tennis  ball  in  which  a  small  hole  has  been  made  by  a  pin  or 
nail.  Result?  In  the  same  way  compare  the  bouncing  of  a  basket 
ball  which  is  just  sufficiently  filled  with  air  to  cause  it  to  keep  its  shape 
with  the  bouncing  of  a  similar  ball  into  which  a  large  amount  of  air  has 
been  pumped. 

From  the  observations  you  have  made  you  will  conclude 
that  the  compressed  air  in  the  automobile  tire  is  able  to  sup- 
port a  great  weight  and  gives  springiness  (elasticity)  to  the 
tire.  Many  tire-filling  compounds  have  been  tried  but  none 
has  been  successful  because  nothing  has  been  found  that 
will  give  the  springiness  possessed  by  compressed  air. 

It  is  evident  that  in  the  construction  of  an  automobile  tire, 
first,  the  tire  must  be  air-tight  to  prevent  the  escape  of  the 
air  and,  second,  it  must  be  of  sufficient  strength  to  resist  the 
pressure  of  the  imprisoned  air.  An  examination  of  an  auto- 
mobile tire  will  show  how  these  two*  requirements  are  met. 
The  inner  tube  made  of  elastic  rubber  is  air-tight.  The  air 
is  pumped  in  through  a  metal  tube  in  which  is  a  valve  that 
will  allow  air  to  be  pushed  in  but  prevents  its  escape. 

The  outer  tire  or  shoe  is  not  necessarily  air-tight  but  pro- 
vides the  strength  to  resist  the  outward  pressure  of  the  con- 
fined air.  It  is  very  strongly  made  of  a  combination  of 
cotton  fabric  or  cord  and  rubber.  In  bicycle  tires  where  the 
weight  supported  is  not  so  great,  frequently  only  one  tube 
is  used.  What  two  properties  must  this  tube  possess? 

Air  is  forced  into  the  tire  by  an  air  pump. 

Problem  3.  How  the  tire  pump  works.  —  If  you  have 
ever  pumped  up  an  automobile  tire,  did  you  find  it  more 


HOW   WE    USE  COMPRESSED   AIR 


21 


FIGURE  22. 
—  BICYCLE 
PUMP. 


difficult  to  work  the  pump  when  the  tire  was 
nearly  empty  or  when  it  was  nearly  filled  ?  In 
the  tire  pump  which  you  used,  was  the  push  or 
the  pull  upon  the  handle  the  harder?  Does  a 
tire  pump  ever  "get  out-of-fix "  or  fail  to 
work? 

Keeping  these  points  in  mind  let  us  examine 
the  diagram  of  an  air  pump  (Figure  22).  As 
the  handle  is  pulled  out,  what  happens  to  the 
air?  Why?  As  the  handle  is  pushed  down, 
what  happens  to  the  air  ?  Why  does  it  not  go 
out  through  the  same  place  through  which  it 
came  in  ?  Why  is  it  more  difficult  to  push  the 
handle  down  than  to  pull  it  up?  Why  is  it 
more  difficult  to  push  the  handle  down  as  you 
continue  to  pump  air  into  the  tire  ? 

The  tire  pump  is  a  very  simple  air  compressor, 

but  air  .  compressors  for  air  brakes, 
pneumatic  drills,  sand  blasts,  and  for 
pumping  air  into  tunnels  where  work  is 
done  under  compressed  air  are  built  on 
the  same  principle. 

Suppose  the  valve  through  which  the 
air  enters  the  pump  should  be  reversed, 
what  would  happen  should  the  nozzle  be 
attached  to  a  basket  ball  and  the  pump 
used?  This  is  the  principle  of  the  ex- 
haust air  pump,  by  which  air  is  pumped 
out  of  a  closed  vessel.  Do  you  think  that 
all  of  the  air  could  be  removed  from  a 
vessel  with  such  a  pump  ?  In  answering 
this,  keep  in  mind  that  however  little  air 


FIGURE  23.  —  FORCE 

PUMP. 

p,  piston ;  c,  cylin- 
der ;  v,  valve ;  D,  dome 
containing  air ;  d,  de- 
livery pipe ;  5,  pump 
stock. 


22 


GENERAL   SCIENCE 


is  in  a  space,  it  will  be  distributed  equally,  filling  all  the 
space. 

Problem  4.  How  a  force  pump  sends  a  steady  stream  of 
water.  —  The  tire  pump  is  really  an  air  force  pump ;  a 
water  force  pump  could  be  made  on  the  same  plan.  Would 


FIGURE  24. —  COMPRESSED  AIR  DRILLS. 
Use  of  compressed  air  drills  in  excavating  a  tunnel  through  solid  rock. 

such  a  water  force  pump  send  a  steady  stream  of  water? 
Such  pumps  are  valuable  in  pumping  water  to  a  tank  on  the 
top  of  a  house  or  into  a  standpipe.  Why  cannot  an  ordinary 
pump  be  used  for  this  purpose  ? 

Some  force  pumps  can  send  a  steady  stream  of  water.     It 
will  be  noticed  that  pumps  of  this  kind  have  connected  with 


HOW   WE    USE  COMPRESSED   AIR 


23 


them  an  iron  dome.  An  examination  of  the  accompanying 
diagram  will  help  us  to  understand  how  this  is  possible 
(Figure  23). 

Explain  what  happens  when  the  piston  (p)  is  pulled  up. 
When  it  is  pushed  down,  what  two  courses  will  the  water 
take  ?  What  will  happen  to  the  air  that  is  in  the  iron  dome  ? 
What  will  this  compressed  air  do  to  the  water  when  the 
piston  starts  upward  and  the  water  is  no  longer  being  forced 


FIGURE  25.  —  RIVETING  HAMMER. 
A,  air  pipe  ;  B,  trigger  for  controlling  the  air;  C,  the  hammer. 

into  the  dome?  What  kind  of  a  stream  will  such  a  pump 
send  out  ?  The  power  of  compressed  air  to  throw  a  stream 
of  water  is  illustrated  by  the  following  experiment. 

Experiment.  —  Half  fill  a  flask  with  water.  Stopper  it  with  a  one- 
hole  stopper  through  which  passes  a  tube  extending  down  below  the 
surface  of  the  water.  Blow  through  the  tube.  What  effect  will  this 
have  upon  the  air  within  the  flask  ?  After  the  air  has  "been  considerably 
compressed,  stop  blowing  into  the  tube  and  observe  what  happens. 

Some  other  important  uses  of  compressed  air  are :  — 
Pneumatic  tubes  for  the  transmission  of  mail,  and  of  cash 


24  GENERAL   SCIENCE 

and  parcels  in  stores;  air  brakes;  pneumatic  drills  and 
riveters ;  and  the  sand  blast  used  in  cleaning  the  fronts  of 
stone  buildings.  Can  you  suggest  any  other  applications  ? 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Construct  a  pump  that  will  send  a  steady  stream  of  water. 

2.  Demonstrate  the  working  of  air  brakes. 

3.  Demonstrate  the  structure  and  the  action  of  pneumatic  drills.  • 

4.  Demonstrate  the  structure  and  the  method  of  working  of  the 
sand  blast  used  in  cleaning  the  outside  of  brick  and  stone  buildings 

REPORT 

Use  of  compressed  air  in  building  bridge  foundations  and  in  the 
construction  of  subways. 


PROJECT  III 
VENTILATION 

do  you  understand  by  ventilation?  We  hear  a 
great  deal  about  the  importance  of  ventilation,  so  that  we 
naturally  ask  ourselves,  why  ventilation  is  so  necessary  and 
how  rooms  may  be  ventilated. 

Problem  1.  Why  rooms  should  be  ventilated.  —  Think 
of  how  you  have  felt  in  rooms  that  were  not  ventilated  and 
in  rooms  that  were  ventilated.  Did  the  fact  that  the  room 
was  empty  or  full  of  people  seem  to  make  any  difference? 
What  effect  do  people  have  on  the  air  of  the  room?  Your 
first  answer  to  this  will  be  that  even  if  pure  air  is  breathed 
in,  impure  or  bad  air  is  being  breathed  out.  What,  then, 
will  be  one  reason  for  the  ventilation  of  a  room  ? 

Another  effect  of  a  crowd  of  people  on  the  air  of  a  room  is 
noticed  when  you  step  from  the  fresh  air  into  a  poorly 
ventilated  room  full  of  people.  Unpleasant  odors  are 
noticed.  These  are  given  off  by  the  mouths,  bodies,  and 
clothing  of  the  persons  in  the  room.  Experiments  have 
shown  that  these  odors  are  not  only  annoying  but  have  a 
bad  effect  on  the  appetite.  What,  therefore,  is  a  second 
reason  for  the  ventilation  of  rooms  in  which  there  are  many 
people  ? 

Another  reason  for  ventilation  may  be  made  clear  by  an 
experience  common  to  us  all.  How  do  you  feel  on  a  hot 
sultry  day  in  summer?  Do  you  feel  different  when  a 
breeze  begins  to  blow?  What  is  the  effect  of  riding  in 

25 


26  GENERAL   SCIENCE 

an  open  trolley  car  or  in  an  automobile  on  such  a  summer 
day? 

The  following  experiment  may  help  us  to  understand  the 
reason  for  this  change  in  feeling. 

Experiment.  —  Put  a  drop  of  ether  on  the  back  of  the  hand.  What 
happens  to  the  ether  ?  How  does  the  spot,  where  the  ether  was,  feel  ? 

Put  a  drop  of  water  on  the  other  hand.  After  it  has  been-  there  a 
few  moments,  fan  the  hand.  Do  you  notice  any  difference  in  tempera- 
ture? The  changing  of  the  ether  and  water  into  a  vapor  or  gas  that 
is  invisible  is  called  evaporation.  What  do  you  conclude  is  the  effect 
of  evaporation  upon  temperature  ? 

Heat  is  being  continually  made  in  the  body.  How  do  you 
suppose  the  body  loses  most  of  its  extra  heat  in  warm  rooms 
and  in  summer  time? 

Evaporation  of  water  goes  on  much  more  slowly  if  there 
is  already  a  large  amount  of  water  vapor  in  the  air.  This 
fact  is  made  clear  to  you  by  the  rapidity  of  the  drying  of 
clothes  on  a  damp  day  and  on  a  dry  day.  In  which  case 
does  the  drying  go  on  more  rapidly  ? 

Experiment.  —  Wet  two  small  pieces  of  cloth ;  hang  one  in  a  dry 
battery  jar  and  the  other  in  a  battery  jar  in  which  there  is  a  small 
amount  of  water.  Which  piece  of  cloth  dries  the  sooner  ?  Conclusion  ? 

It  is  estimated  that  each  person  gives  off  from  his  mouth 
and  skin  about  three  pints  of  water  daily  and  about  as  much 
heat  as  is  produced  by  a  candle  flame.  Of  course,  if  exercise 
is  being  carried  on,  both  more  moisture  and  more  heat  are 
given  off.  What,  therefore,  will  be  the  condition  of  a  poorly 
ventilated  room  in  which  there  are  a  number  of  persons? 

It  is  an  accepted  fact  that  the  dullness  and  drowsiness 
felt  in  such  a  room  are  due  chiefly  to  the  heat  and  moisture. 
Experiments  have  shown  that  men  do  15  per  cent  less  work 
at  a  temperature  of  75  degrees  F.  and  37  per  cent  less  work 


VENTILATION 


27 


at  86  degrees  F.  than  at  68  degrees  F.  In  warm  rooms  the 
blood  comes  to  the  surface  of  the  body.  Why  ?  What  effect 
will  this  have  upon  the  amount  of  blood  that  goes  to  the 
brain?  What  will  be  the  result?  In  the  same  way,  the 
blood  vessels  in  the  nostrils  become  congested,  making 
an  ideal  condition  for  the  growth  of  germs.  As  a  result, 
people  who  live  in  overheated  rooms  usually  have  colds. 
The  proper  temperature  for  a  room  is  68  to  70  degrees  F. 

Although  a  poorly 
ventilated  room  contain- 
ing many  people  is  likely 
to  have  too  much  mois- 
ture in  the  air,  there  is 
danger  in  the  winter  of 
having  too  little  moisture 
in  the  air;  this  is  espe- 
cially true  in  apartments 
occupied  by  only  a  few 
people.  It  is  advisable 
under  these  circum- 
stances to  keep  on  the 
radiator  or  stove  a  basin 
of  water  which  will  sup-  .  FlGURE  26.  — ELECTRIC  FAN. 

ply  moisture  to  the  air 

by  its  evaporation.     Hot  air  furnaces  have  a  special  water 

basin  which  should  be  kept  filled  if  the  occupants  of  the 

house  are  to  enjoy  the  maximum  of  comfort  and  well-being. 

Briefly  summarize  the  reasons  for  ventilating  a  room. 

Problem  2.  How  air  in  a  room  may  be  set  in  motion.  — 
One  method  of  keeping  the  air  of  a  room  in  motion  is  by  the 
use  of  fans  (Figure  26).  Explain  why,  in  summer,  one  feels 


28 


GENERAL  SCIENCE 


so  very  much  better  in  an  office,  room,  or  subway  car  in  which 
an  electric  fan  is  in  motion.     Recall  how  quickly  one  feels  the 
change  when  the  fan  is  shut  off.    Why  is  ventilation  of  a  room 
entirely  by  an  electric  fan  not  a  perfect  method  ? 
What  is  not  provided  for  by  such  ventilation? 
We  know,  however,  that  most  ventilating 
systems  do  not  depend  on  fans.     The  question 
then  is,  how  may  a  circulation  of  the  air  be 
caused,  when  fans  are  not  used.     The  follow- 
ing experiments  may  help  us  to  answer  this 
FIGURE  27.       question. 

Experiment.  —  Put  a  lighted  candle  in  the  bottom  of  an  uncovered 
battery  jar.     Light  a  stick  of  Chinese  punk  or  incense  and  hold  it 
near  the  top   of  the   jar.      What 
happens  ?    What  do  you  think  may 
be  the  cause  of  this  ? 

Experiment.  —  To  find  out  the 
effect  of  heat  on  the  weight  of  air, 
place  a  lighted  Bunsen  burner  near 
one  of  the  scale  pans  of  a  sensitive 
balance.  Result  ?  Conclusion  ? 
The  reason  for  this  is  made  clear 
by  the  following  experiment. 

Experiment.  —  To  find  out  how 
heating  air  makes  it  lighter,  pass  a 
glass  tube  through  the  stopper  of  a 
flask.  Take  care  that  the  stopper 
is  air-tight.  Invert  the  flask,  plac- 
ing the  outer  end  of  the  glass  tube 
under  water.  Gently  heat  the  flask 
(Figure  27).  Result?  Conclusion? 


FIGURE  28. —  CURRENTS  OF  AIR  IN 
A  REFRIGERATOR. 


The  currents  of  air  caused  by  heat  are  called  convection 
currents.  These  currents  of  air  are  well  illustrated  by  move- 
ments of  air  in  a  refrigerator  (Figure  28). 


VENTILATION 


29 


Problem  3.  How  convection  currents  may  be  used  in 
ventilating  a  room. —  Windows  are  very  frequently  de- 
pended upon 'for  ventilation. 

Experiment.  —  To  find  out  the  best  arrangement  of  windows  for 
good  ventilation  of  a  room,  take  a  wooden  soap  box  or  a  starch  box. 
Across  the  front  of  the  box  place  a  piece  of  glass 
so  that  it  may  act  as  a  sliding  door.  In  each  end 
of  the  box  bore  four  holes  so  arranged  as  to  repre- 
sent the  upper  and  lower  parts  of  windows. 
Provide  corks  for  these  openings.  Place  inside  of 
the  box  one  or  more  candles.  Light  the  candles. 
Allow  all  the  lower  holes  to  remain  open.  Note 
the  result.  Try  various  combinations.  What  is 
your  conclusion  as  to  the  best  way  to  ventilate  a 
room  by  means  of  windows  ? 

If  the  air  outside  is  cooler  than  the  air 
inside  the  room,  and  the  window  is  open  at 
both  top  and  bottom,  where  does  the  air 
enter  and  where  does  it  leave  (Figure  29)  ? 
Explain. 

A  draft  or  a  direct  current  of  air  striking 
against  the  body  is  apt  to  induce  a  cold 
since  that  portion  of  the  body  is  cooled 
so  completely  that  the  blood  coming  there 
is  forced  into  some  other  part,  causing  a 
congestion  which  affords  a  favorable  condi- 
tion for  the  growth  of  bacteria  or  germs 
that  cause  colds. 

With  a  window  open  at  the  top  and  bottom,  would  the 
greater  danger  of  draft  be  from  the  top  ?  Suggest  means  of 
protecting  persons  from  a  draft  in  a  room  ventilated  in 
this  way. 

Explain  how  a  stove  or  fireplace  will  help  in  the  ventilation 


FIGURE  29. — VENTI- 
LATION BY  WINDOW. 

Window  open  at 
both  top  and  bot- 
tom. 


30 


GENERAL   SCIENCE 


of  a  room  (Figure  30).  Make  a  diagram 
of  a  room  containing  a  fireplace  and  indi- 
cate by  arrows  the  direction  of  the  air  in 
the  room. 

How  are  your  rooms  at  home  ventilated 
in  summer  ?  In  winter  ?  Make  diagrams 
of  the  summer  and  winter  ventilation  of 
one  room. 

Modern  office  buildings,  and  sometimes 
schools,  are  heated  and  ventilated  by  air 
being  forced  into  them  by  fans  through 
large  pipes.  If  the  air  comes  in  heated, 
ought  the  inlet  to  be  at  the  top  or  bottom 
of  the  room?  Where  ought  the  outlet 
to  be? 

Experiments  and  observations  have 
shown  that  the  health  is  much  better  if  sleeping  rooms  are 
well  ventilated  and  kept  at  a  relatively  low  temperature, 
provided  that  the  body  is  not  in  a  draft  and  is  properly 
protected  to  prevent  its  becoming  chilled. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Carry  out  a  series  of  experiments  to  show  the  direction  of  air 
currents  in  a  room.     Show  results  in  a  diagrammatic  drawing  of  the 
room.     Do  this  for  different  rooms  of  your  house. 

2.  Carry  out  a  plan  to  prevent  a  draft  in  a  room  ventilated  by 
windows. 


FIGURE  30.  —  FIRE- 
PLACE. 

What  causes  the  air 
to 'go  up  the  flue? 


PROJECT  IV 
WINDS 

SINCE  winds  are  movements  of  air,  you  would  naturally 
suspect  that  they  may  be  caused  in  the  same  way  as  the  air 
currents  of  ventilation.  In  considering  the  cause  of  winds 
you  will  at  once  think  of  different  kinds  of  winds,  such  as 
sea  breezes,  gentle  breezes  that  seem  to  come  from  any  direc- 
tion, violent  gales,  trade  winds,  hurricanes  and  tornadoes. 
Does  it  seem  probable  that  all  these  winds  are  caused  by 
the  unequal  heating  of  the  air? 

Problem  1.  How  sea  breezes  are  caused.  —  Anyone 
living  within  a  few  miles  of  the  sea  coast  is  familiar  with  the 
breeze  that  springs  up  on  hot  days  in  summer.  Since  this 
wind  occurs  only  on  hot  days  and  dies  down  toward  evening, 
being  replaced  frequently  during  the  night  by  a  breeze  from 
the  land  to  the  ocean,  you  will  suspect  that  in  some  way  it  is 
concerned  with  heat. 

If  this  wind  is  caused  in  the  same  way  that  air  currents  of 
ventilation  are  produced,  there  must  be  an  unequal  heating 
of  the  land  and  water.  Do  you  think  that  the  ocean  and 
the  land  receive  different  amounts  of  heat  from  the  sun? 
The  problem  to  be  solved,  therefore,  is,  how  the  unequal 
heating  can  be  accounted  for. 

Experiment.  —  Put  into  different  drinking  glasses  or  beaker  glasses 
equal  quantities  of  -water  and  earth.  Put  them  into  an  oven  for  about 
twenty  minutes.  On  removal  put  into  each  beaker  glass  a  thermometer. 

31 


32 


GENERAL   SCIENCE 


Note  the  temperature  when  first  removed  from  the  oven  and  at  inter- 
vals of  ten  or  fifteen  minutes.     Result  ?     Conclusion  ? 
Explain 'now  the  cause  of  sea  breezes. 

The  seasonal  or  monsoon  winds  of  India  are  accounted  for 
in  a  similar  manner.  During  the  summer  the  land  becomes 
highly  heated  and  winds  blow  from  the  Indian  ocean  to 


FIGURE  31.  —  SUMMER  MONSOON.         FIGURE  32.  —  WINTER  MONSOON. 

the  land,  while  in  winter  the  water  is  warmer  than  the  land 
and  the  direction  of  the  wind  is  reversed. 

Considering  the  fact  that  land  becomes  warmed  more 
rapidly  and  cools  more  rapidly  than  'water,  explain  the 
following : 

1.  Why  New  York  City  has  a  later  spring  than  places  in 
Ohio  and  Indiana  which  are  no  farther  north  or  south. 

2.  Why  the  region  along  Lake  Ontario  is  better  for  raising 
fruit  than  places  much  farther  south. 

On  the  diagram  representing  the  world's  winds  note  the 
direction  of  the  trade  winds.  Why  do  they  blow  toward  the 
equator  ?  The  fact  that  they  blow  from  the  southeast  and 
northeast  rather  than  directly  from  the  north  and  south 
is  due  to  the  rotation  of  the  earth.  In  the  northern  hem- 
isphere the  winds  are  deflected  to  the  right  and  in  the 
southern,  to  the  left. 


WINDS 


33 


Problem  2.  Why  our  winds  vary  in  direction  and  velocity. 
—  Note  the  direction  of  the  winds  in  your  locality  for  a  few 
days.  Do  they 
always  come  from 
the  same  direc- 
tion ?  Do  they 
always  seem  to 
come  from  a  cooler 
to  a  warmer  place  ? 
Do  you  think  that 
they  are  caused  in 
the  same  way  as 
sea  breezes? 

Reference  again 
to  the  diagram  of 
world's  winds  may 
help  us.  In  what 
general  direction 


\     \ 
V>e4ta/F 


FIGURE  33.  —  THE  WORLD'S  WINDS. 


are   the   winds   of   the   part    of   the    world    in    which    we 
live?    These  winds  are  called  the  prevailing  westerlies. 

Because  of  inequalities 
of  heating  and  irregulari- 
ties of  surface,  low  pres- 
sure areas  develop  in  this 
general  current  (the  pre- 
vailing westerlies) .  As 
the  air  rushes  in  toward 
a  low  pressure  area  a 

whirlpool  is  formed  such 
FIGURE  34.  — PROGRESS  OF  A  STORM      as    you   may    see    as    tne 

CENTER.  •  '   V  j 

Note  the  rate  of  speed  of  this  storm        Water  1S  dramed  fr°m  ^ 
center.  bath  tub,  or  in  the  dust 


36 


GENERAL  SCIENCE 


whirls  which  occur  in  the  road  in  summer.  The  low  pressure 
which  started  the  dust  whirl  is  formed  by  the  excessive 
heating  of  a  small  area  of  the  road. 

These  low  pressure  areas  which  develop  in  the  prevailing 
westerlies  travel  with  the  westerlies  in  a  general  direction 
from  west  to  east  (Figures  34  and  37).  The  air  for  hun- 
dreds of  miles  passes  in  toward  a  low  pressure  area,  not 


FIGURE  37.  —  USUAL  PATHS  OF  "  HIGHS"  AND  "Lows." 

directly  but  in  a  spiral,  just  as  water  does  when  drained 
from  a  bath  tub.  These  great  whirls  of  air,  which  are  con- 
tinually passing  across  the  country,  are  called  cyclones;  and 
most  of  our  winds  are  portions  of  these.  The  cyclones, 
of  course,  are  separated  by  areas  of  high  pressure  (Figures 
35  and  36). 

Directly  in  the  center  of  a  low  pressure  area,  in  what 
direction  do  the  currents  of  air  flow?  What  is  the  direction 
of  these  currents  in  the  center  of  a  high  pressure  area? 


WINDS  37 

Which  is  warmer,  an  area  of  low  pressure  or  an  area  of 
high  pressure?  Low  pressure  areas  are  cloudy  and  rainy. 
High  pressure  areas  are  clear. 

Tornadoes  are  violent  wind  storms,  and  are  sometimes 
wrongly  called  cyclones.  They  are  usually  not  more  than 
40  to  500  yards  in  width.  In  tornadoes  the  air  is  rushing 
spirally  upward  at  a  rate  of  100  to  400  miles  per  hour.  Di- 
rectly in  the  center  of  the  tornado  there  is  a  very  much 


Photograph  by  F.  Cundill. 

FIGURE  38. — TORNADO. 
This  tornado  was  seen  near  Isabel,  South  Dakota,  June  25,  1914. 

lessened  air  pressure.  The  condensation  of  moisture  within 
this  area  of  lessened  pressure  and  the  presence  of  dirt  carried 
up  by  the  air  cause  the  funnel  shaped  cloud  which  is  char- 
acteristic of  this  kind  of  storm  (Figure  38). 

But  a  cyclone  is  an  entirely  different  kind  of  storm. 
Compare  a  tornado  and  a  cyclone  as  to  size.  Tornadoes 
usually  occur  in  the  southeastern  part  of  a  cyclone  and 
move  toward  the  northeast,  which  is  the  direction  of  the 


38 


GENERAL   SCIENCE 


prevailing  wind  in  that  part  of  a  cyclone.     They  travel  at 
the  rate  of  20  to  50  miles  an  hour. 

Tornadoes  are  very  destructive,  frequently  destroying 
everything  in  their  paths  (Figure  39).  Trees  may  be 
completely  demolished ;  large  stones  and  even  locomotives 
have  been  known  to  be  carried  a  considerable  distance; 
straws  have  been  driven  into  wood  as  though  they  were 


FIGURE  39.  —  RESULTS  OF  A  SEVERE  WINDSTORM. 

nails,  and  many  other  astounding  results  have  been  known 
to  occur.  Frequently  the  walls  of  buildings  near  which  the 
center  of  the  storm  passes  fall  outward  as  though  from 
an  explosion.  Explain  this.  Waterspouts  are  whirlwinds 
over  the  ocean. 

Problem  3.  What  are  hurricanes? — Hurricanes  are 
similar  to  cyclones  but  are  usually  of  less  extent  and  more 
violent.  They  form  over  the  ocean.  The  ones  that  affect 
us  originate  near  the  West  Indies  and  move  toward  the 


WINDS 


39 


80° 


3V* 


FIGURE  40.  —  PATH  OF  A  HURRICANE. 


northwest  until  the  coast  of  the  United  States  is  reached. 
They  then  move  toward  the  north  and  northeast,  paral- 
lel with  the  coast,  finally  passing  eastward  out  into  the 


40 


GENERAL   SCIENCE 


Atlantic  Ocean  (Figure  40).  Occasionally,  one  of  these 
hurricanes  passes  into  the  Gulf  of  Mexico.  Galveston, 
Texas,  was  nearly  destroyed  in  1900  by  the  waves  pro- 
duced by  such  a  hurricane.  Similar  storms  in  the  Pacific 
and  Indian  oceans  are  called  typhoons. 

Thunderstorms  frequently  develop  at  the  close  of  a  hot, 
sultry  day.    They  are  caused  by  the  rising  of  hot,  moist 


FIGURE  41.  —  CUMULUS  CLOUDS. 


Photograph  by  McAdie. 


air.  The  moisture  of  the  air  condenses  into  dome-shaped, 
white  clouds  known  as  cumulm  clouds  (Figure  41).  The 
downpour  of  water  is  accompanied  or  preceded  by  a  set- 
tling downward  of  the  cooler  air  which  pushes  out  from 
all  sides  of  the  storm  area,  forming  the  strong  wind  of  the 
approaching  thunderstorm.  After  the  thunderstorm  has 
passed,  the  temperature  is  usually  cooler,  largely  because  of 
this  settling  of  the  cooler  air  from  above. 


WINDS 


41 


Thunderstorms  usually  occur  in  the  southeastern  portion 
of  a  low  pressure  area,  and  move  in  an  easterly  direction  at 
the  rate  of  20  to  50  miles  an  hour.  The  storm  is  preceded 
as  it  travels  by  a  sheet  of  clouds  advancing  at  a  rather  high 
elevation.  As  the  storm  draws  near,  there  appears  the 
black  mass  of  the  main  storm  cloud.  Soon  the  dense  cur- 
tain of  rain  may  be  seen  pouring  from  its  base  (Figure 


FIGURE  42.  —  THUNDERSTORM. 

Photographed  by  Lieutenant  W.  F.  Reed,  Jr.,  U.  S.  N.  R.  F.,  near  Pensa- 
cola,  Florida,  August,  26,  1918.  (Published  by  permission  of  the  Navy 
Department.)  .,  '£& 

42).     Along  the  front  of  the  rain  there  is  often  a  low  cloud, 
ragged  and  torn  by  the  wind. 

A  short  time  after  the  rain  ceases,  sometimes  even  before, 
the  sky  may  begin  to  clear ;  and  the  sun  shining  on  the  de- 
parting rain  curtain  gives  us  one  of  the  most  beautiful  and 
wonderful  spectacles  of  Nature,  the  rainbow.  Then  the  storm 
cloud,  illumined  by  the  sun,  may  be  seen  passing  eastward. 


42  GENERAL   SCIENCE 

Problem  4.  How  the  weather  bureau  is  able  to  predict 
the  weather.  —  Examine  weather  maps.  Note  the  direc- 
tion of  winds,  temperature,  raininess  or  cloudiness,  and  low 
and  high  pressure  areas.  Suggest  a  basis  for  the  weather 
predictions  issued  by  the  U.  S.  Weather  Bureau. 

Explain  how  a  barometer  enables  one  to  forecast  the 
weather  for  a  short  time  in  advance. 

What  two  factors  are  important  in  determining  the  veloc- 
ity of  a  wind  at  any  one  point  ? 

Explain  how  a  hot  wave  may  be  caused  by  a  cyclone. 
Explain  how  a  blizzard  or  "  norther  "  may  be  caused  by  a 
cyclone.  Suggest  the  relation  between  a  cold  wave  and  a 
high  pressure  area. 

The  United  States  Weather  Bureau  has  nearly  200  ob- 
servation stations  throughout  the  United  States  and  Canada, 
at  which  simultaneous  records  of  barometric  pressure,  tem- 
perature, direction  and  velocity  of  the  wind,  the  rain  or 
snowfall  and  cloudiness,  are  made.  These  observations 
are  telegraphed  to  Washington  and  from  there  the  collected 
information  is  sent  to  the  various  stations  where  weather 
maps  showing  the  weather  conditions  in  all  parts  of  the 
country  are  made.  The  forecasters  study  these  maps  and 
are  able  to  forecast  the  probable  weather  conditions  for  the 
next  24  or  48  hours  (Figures  35  and  36). 

By  means  of  telegraph,  telephone,  wireless,  and  mail  or  by 
means  of  flags  or  steam  whistles  the  daily  forecasts  -reach 
every  part  of  the  country  in  a  surprisingly  short  time. 

Special  warnings  of  frost  and  the  approach  of  a  cold  wave 
are  sent  to  farming,  gardening,  and  fruit  districts  and  to 
railroads  and  to  shippers  of  vegetables  and  livestock.  Warn- 
ings of  gales  along  coasts  and  on  the  Great  Lakes  are  sent  to 
shipping  offices  and  to  vessels. 


WINDS  43 

SUGGESTED  INDIVIDUAL  TOPICS 

1.  Keep  a  daily  record  of  temperature,  air  pressure,  direction,  and 
approximate  velocity  of  the  wind,  cloudiness,  and  rain-  or  snowfall. 
In  connection  with  these  observations  study  the  maps  of  the  United 
States  Weather  Bureau. 

2.  Make  a  toy  windmill  and  use  it  in  running  a  simple  machine. 

REPORTS 

1.  The  work  of  the  United  States  Weather  Bureau. 

2.  An  account  of  the  hurricane  that  caused  so  much  damage  to 
Galveston,  Texas. 

3.  An  account  of  a  tornado. 

REFERENCES  FOR  PROJECT  IV 

1.  Weather  and  Weather  Instruments,  P.  R.  Jameson.     Taylor 
Instrument  Company,  Rochester,  N.  Y.,  50  cents. 

2.  Practical  Hints  for  Amateur  Weather  Forecasters,  P.  R.  Jame- 
son.    Taylor  Instrument  Company,  10  cents. 

3.  Instructions  for  Volunteer  Observers.     U.  S.  Weather  Bureau, 
Washington. 

4.  Practical  Exercises  in  Elementary  Meteorology,  Ward.     Ginn  & 
Co. 

6.  About  the  Weather,  Mark  W.  Harrington.     D.  Appleton  &  Co. 

7.  The  Weather  and  Climate  of  Chicago,  Cox  and  Armington, 
University  of  Chicago  Press. 

8.  The  Wonder  Book  of  the  Atmosphere,  E.  J .  Houston.    Frederick 
A.  Stokes  Co. 

9.  Our  Own  Weather,  Martin.     Harper  &  Bros. 

10.  Reading  the  Weather,-  T.  M.  Longstreth.    Outing  Publishing 
Co. 


^  '•  PROJECT  V 

HOW  WE  HEAR 

THINK  a  moment  of  what  you  would  miss  and  how  you 
would  be  handicapped  if  you  were  unable  to  hear.  Make  a 
list  of  ten  examples  in  which  inability  to  hear  would  affect 
you. 

In  considering  how  we  hear,  there  are  several  things  which 
are  at  once  evident ;  first,  there  is  always  a  sound  of  some 
kind ;  second,  the  sound  may  be  reproduced  or  heard  at  some 
distance  from  the  place  where  it  was  originally  produced; 
third,  we  have  a  special  organ,  the  ear,  which  receives  the 
sound.  In  working  out  this  project,  therefore,  it  will  be 
necessary  to  know  just  what  sound  is,  how  sound  may 
travel  and  be  reproduced  and  how  the  human  ear  is  fitted 
to  receive  sounds. 

Problem  1.  What  sound  is.  —  Think  of  the  different 
ways  in  which  sound  is  produced.  How  is  a  drum  made  to 
give  out  sound  ?  What  is  the  effect  of  putting  the  hand  on 
the  head  of  the  drum  while  it  is  sounding?  A  violin  or 
banjo  gives  out  sound  when  a  string  is  pulled  to  one  side  and 
then  released.  If  the  string  is  looked  at  carefully,  it  will 
be  seen  to  be  vibrating.  What  happens  the  moment  you 
stop  these  vibrations  by  touching  the  string  ? 

Experiment.  —  Touch  the  surface  of  water  in  a  glass  with  the  tips 
of  a  tuning  fork  which  is  sounding  (Figure  43).  Result?  Conclusion? 

An  examination  of  all  bodies  giving  out  sound  will  lead 
us  to  the  conclusion  that  sound  always  originates  as  a  vi- 

44 


HOW   WE  HEAR 


45 


bration.  The  vibrating  bodies  cause  air  waves  very  much 
as  the  vibrating  tuning  fork  produced  waves  in  the  water 
in  the  glass. 

Experiment.  —  Blow  diagonally  into  a  small  bottle  or  test  tube. 
Use  tubes  and  bottles  of  various  sizes.  Result?  In  this  experiment 
air  waves  are  produced  directly. 

It  is  in  this  way  that  sound  is  produced  in  such  instru- 
ments as  the  organ,  flute,  cornet,  and  trombone.  The  sound 
here  is  produced  by  the  vibration  of  columns  of  air. 

In  what   three  ways   do   sounds  differ?    Naturally  we 
wonder,    what    are    the    causes   of 
these  differences. 

Experiment.  —  Compare  the  sound 
(note)  given  by  a  violin  or  other  stringed 
instrument  when  the  strings  are  stretched 
very  tightly  and  when  the  strings  are 
stretched  less  tightly.  By  holding  the 
finger  on  the  string  permit  only  a  portion 
of  it  to  vibrate.  Result  ?  Set  into  vibra- 
tion one  of  the  very  slender  strings  of  a 
violin  or  guitar  and  one  of  the  thicker 
ones.  Even  though  they  are  of  the  same 
length  and  of  the  same  tension  or  tight- 
ness, what  is  the  result?  FIGURE  43. 

A  careful  examination  will  show  that  in  every  case  where 
the  tone  or  pitch  was  high,  the  vibrations  were  more  rapid 
than  when  a  lower  pitch  was  produced.  You  will  also  re- 
call that  blowing  into  very  small  bottles  gave  a  much 
higher  pitch  than  blowing  into  larger  ones.  This  was  be- 
cause the  air  vibrations  produced  in  the  smaller  bottles  were 
more  rapid. 

If  you  look  at  the  arrangement  of  strings  of  a  piano,  you 
will  find  that  they  are  not  all  of  the  same  length ;  the  ones 


46 


GENERAL   SCIENCE 


which  give  out  the  low  tones  being  long  and  thick,  and  those 
which  produce  the  high  tones,  short  and  thin. 

The  human  voice  illustrates  this  very  well.  Children  have 
high-pitched  voices,  but  boys'  voices  usually  become  deeper 
or  lower-pitched  when  they  are  about  fourteen  years  old. 
This  is  because  the  voice  box,  or  "  Adam's  apple,"  of  the 
boy  becomes  considerably  larger  at  this  time,  and  the  vocal 
cords  become  longer  and  larger,  and  therefore  vibrate  more 

slowly,  producing  a  lower 
tone.  The  voice  box  of 
a  girl  does  not  usually 
grow  much  larger  as  she 
gets  older,  and  conse- 
quently the  voice  of  a 
woman  remains  high- 
pitched. 

If  you  are  beating  a 
drum  and  wish  to  make 
a  louder  sound,  what  do 
you  do?  If  some  one  is 
sleeping  and  you  do  not 
wish  to  disturb  him,  how 
do  you  walk  across  the 
floor? 

The  loudness  of  sound  is  caused  by  the  width  of  the  vi- 
bration. Compare  the  sound  given  by  the  string  of  a  violin 
when  it  is  set  into  gentle  vibrations  with  the  sound  produced 
when  the  vibrations  are  greater.  It  will  be  noticed  that  the 
tone  or  pitch  remains  the  same,  but  that  there  is  a  great 
difference  in  loudness  or  volume. 

The  quality  of  the  sound  is  due  largely  to  secondary  vi- 
brations (overtones)  which* vary  with  the  character  of  the 


FIGURE  44. —  ONE  OF  THE  EARLIEST 
TALKING  MACHINES. 


HOW   WE  HEAR 


47 


sounding  bodies.  Hence,  sounds  of  the  same  pitch  and 
loudness  produced  by  piano,  violin,  guitar,  or  organ,  have 
distinctive  qualities.  This  is,  of  course,  the  main  reason 
for  having  many  kinds  of  instruments  in  an  orchestra. 

Briefly  summarize  your  conclusions  as  to  what  sound  is 
and  the  cause  of  differences  in  pitch,  loudness,  and  quality 
of  sounds. 


FIGURE  45.  —  PHONOGRAPH. 

Note  the  sound  box,  to  which  is  attached  a  needle  which  runs  in  the  groove 

of  the  record. 

Problem  2.  How  a  phonograph  reproduces  sound.  — 
To  understand  how  the  voice  of  Caruso,  the  music  of  the 
violin  of  Mischa  Elman  or  of  a  wonderful  church  choir  may 
be  reproduced  in  our  own  home  by  the  phonograph,  it  will 
be  necessary  to  consider  how  the  record  is  made. 

The  essential  part  of  a  phonograph  is  the  sound  box  with 


48 


GENERAL   SCIENCE 


its  diaphragm  which  is  similar  to  the  head  of  a  drum 
(Figure  45).  To  the  center  of  the  diaphragm  is  attached  a 
rod  which  transmits  to  a  needle  any  movement  of  the  drum 
head  or  diaphragm.  Every  vibration  of  the  vocal  cords  of 
the  singer  or  of  the  strings  of  the  violin  produces  in  some 


FIGURE  46.  —  MICRO- PHOTOGRAPH  OF  PORTION  OF  A  RECORD. 

way  a  similar  vibration  of  the  diaphragm  which  transmits 
the  vibration  to  the  needle  which  in  turn  leaves  a  record  on 
a  revolving  wax  plate  upon  which  it  rests  (Figure  46). 
Copies  of  the  wax  plates  made  of  hard  material  are  the 
records  which  we  buy  (Figure  47).  How  the  vibrations 


HOW   WE  HEAR 


49 


of  the  diaphragm,  located  many  feet  from  the  source  of 
the  sound,  are  caused  is  a  problem  to  be  solved.  Evidently 
there  is  nothing  but  air  to  carry  the  vibrations. 


FIGURE  47. —  PHONOGRAPH  RECORD. 
An  original  wax  impression  of  a  phonograph  record. 

Experiment :  Does  air  conduct  sound  ?  —  Through  the  stopper  of 
a  wide-mouthed  bottle  pass  two  wires  connected  with  several  dry  cells 
and  a  key  for  closing  the  circuit.  (Care  should  be  taken  to  make  the 
stopper  air-tight.)  Attach  the  ends  of  the  wires  to  the  binding  posts 
of  an  electric  bell.  Place  the  bell  in  the  bottle,  insert  the  cork,  and 
close  the  circuit.  Can  you  hear  the  ringing  of  the  bell  ?  Now  put  a 
small  amount  of  water  in  the  bottle  and  heat  it  until  the  steam  drives 


50 


GENERAL   SCIENCE 


out  the  air,  put  the  stopper  into  the  bottle  and,  after  the  bottle  has 
cooled,  again  close  the  circuit.  Do  you  hear  the  ringing  as  before? 
Allow  air  to  enter  the  bottle  gradually.  As  it  does  so,  do  you  notice 
any  difference  in  the  sound  of  the  bell  ?  Conclusion  ? 

As  the  finished  record  revolves  under  the  needle,  all  the 
movements  of  the  original  needle  are  reproduced  and  corre- 
sponding vibrations  are  set  up  in  the  diaphragm  of  the  sound 
box.  These  in  turn  cause  air  waves 
like  the  original  ones  and  we  may 
enjoy  wonderful  musical  treats  which 
in  most  cases  would  otherwise  be 
unattainable. 

In  the  telephone  the  air  waves  pro- 
duced by  the  voice  cause  vibrations 
of  the  diaphragm  in  the  telephone 
transmitter  (Figure  48) .  By  means  of 
an  electro-magnet,  concerning  which 
we  shall  learn  more  later,  electric 
currents  varying  according  to  the 

phragm,  held  around  its    vibrations  of  the  diaphragm  are  trans- 
edge  by  a  soft  rubber  ring ;        .        ,        ,  ,  ,      , 
A  and  B.  parallel  carbon    mitted    along    the    telephone    wire. 
plates,  separated  by  carbon    These  currents  cause  the  diaphragm 
in  the  telephone  receiver  to  vibrate  in 

the  same  way  as  the  one  in  the  transmitter,  and  air  waves 
are  set  up  corresponding  to  the  air  waves  produced  by  the 
voice  of  the  person  speaking  into  the  telephone  miles  away. 

Problem  3.  How  the  ear  is  fitted  to  receive  sounds.  — 
The  way  in  which  the  ear  is  able  to  receive  sound  waves 
may  be  understood  by  a  study  of  the  diagram  showing  the 
arrangement  of  the  parts  of  the  ear.  The  external  portion, 
which  is  roughly  funnel-shaped,  leads  into  a  tube  about  an 


FIGURE  48. — TELEPHONE 
TRANSMITTER. 

M,  mouthpiece  ;  F  and 
C,  front  and  back  of  metal 
case ;  D.  aluminum  dia- 


HOW   WE  HEAR  51 

inch  in  length  at  the  end  of  which  is  the  ear  drum.  Beyond 
the  ear  drum  is  the  middle  ear  which  connects  with  the  throat 
by  the  Eustachian  (u-sta/  ki-an)  tube.  Across  the  cavity  of 
the  middle  ear  extends  a  chain  of  very  small  bones,  one  end 
of  which  is  in  contact  with  the  ear  drum,  and  the  other  with 
the  membrane  of  the  inner  ear.  In  the  inner  ear,  which  is 


FIGURE  49. —  HUMAN  EAR. 

1,  external  ear ;  2,  hairs  at  entrance  of  auditory  canal ;  3,  auditory  canal  ; 
4,  semicircular  canal,  a  portion  of  internal  ear ;  5,  auditory  nerve  leading 
to  the  brain ;  6,  ear  drum,  from  which  a  chain  of  bones  extends  to  the 
inner  ear ;  9,  Eustachian  tube,  connecting  the  middle  ear  with  the  throat. 

filled  with  liquid,  are  many  minute  projections  of  a  large 
nerve,  the  auditory  nerve,  which  extends  to  the  brain. 

Your  knowledge  of  the  way  in  which  sound  waves  act 
will  enable  you  to  explain  what  goes  on  in  the  ear  when  air 
waves  reach  it  (Figure  49).  What  is  the  advantage  of 
the  expanded  outer  portion  of  the  ear?  What  effect  will 


52  GENERAL   SCIENCE 

the  air  waves  have  upon  the  ear  drum  ?  What  is  the  pur- 
pose of  the  chain  of  bones  in  the  middle  ear?  What  will 
happen  to  the  liquid  in  the  inner  ear  as  a  result  of  the 
movement  of  the  chain  of  bones?  The  small  nerve  fila- 
ments are  affected  by  the  motion  of  the  liquid  surrounding 
them,  and  a  message  is  carried  to  the  brain  by  the  auditory 
nerve.  Thus  we  have  the  sensation  of  hearing. 

The  purpose  of  the  Eustachian  tube  is  to  equalize  the 
pressure  of  the  air  on  the  two  sides  of  the  ear  drum  so  that 
it  will  vibrate  freely.  Sometimes  in  yawning  you  will 
notice  that  for  a  moment  you  cannot  hear  distinctly  and  that 
you  have  a  peculiar  ringing  in  the  ears.  This  is  because 
the  tubes  have  become  temporarily  closed.  The  same  con- 
dition may  arise  for  a  longer  time  as  a  result  of  a  cold. 

The  peculiar  feeling  in  the  ears  experienced  in  going  up  or 
down  in  an  elevator  in  a  high  building  or  through  a  tunnel, 
is  due  to  the  fact  that  the  pressure  of  the  air  on  one  side 
of  the  ear  drum  is  greater  than  that  on  the  other.  Open- 
ing the  mouth  or  swallowing  will  relieve  the  pressure. 
Why?  Artillerymen  are  apt  to  have  their  ear  drums 
broken  at  the  time  of  firing  their  guns  unless  they  open 
their  mouths.  Explain. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.-  Demonstrate  the  structure  and  the  method  of  production  of 
sound  by  one  of  the  following  musical  instruments :  violin,  guitar, 
banjo,  cornet,  flute,  drum,  piano,  organ,  etc. 

2.  The  dictograph. 

3.  How  the  player-piano  works. 

4.  Construct  a  telephone  to  be  used  between  two  rooms  of  the  school 
building. 

5.  Construct  a  speaking  tube  between  two  classrooms. 

6.  Construct  the  model  of  a  human  ear. 


HOW   WE  HEAR  53 

REPORTS 

1.  The  history  of  the  development  of  certain  musical  instruments. 

2.  Discovery  and  development  of  the  talking  machine. 

3*   Different  kinds  of  organs  of  hearing  possessed  by  animals. 
4.  The  Maxim  "  silencer  "  for  firearms. 


PROJECT  VI 


IMPORTANCE  TO   US   OF   OXIDATION   (BURNING) 

WE  realize  that  burning  is  of  great  importance  to  us 
when  we  consider  that  it  furnishes  us  with  heat,  light,  and 
power.  When  properly  controlled,  it  is  one  of  our  most  use- 
ful servants;  but  when 
it  is  uncontrolled,  it  be- 
comes one  of  our  most 
destructive  enemies. 


Problem  1.  What 
burning  is.  —  We  build 
a  bonfire  or  a  fire  .in  a 
stove  for  the  heat  it  pro- 
duces. Fires  on  hilltops 
have  been  used  from  the 
earliest  times  as  night 
signals.  What,  therefore, 
may  we  say,  is  produced 
by  burning? 

If  the  draft  of  the 
stove  or  furnace  is  good, 
the  fire  burns  brightly; 


FIGURE  50.  —  OIL  FIRE. 
Burning  of  a  55,000  barrel  oil  tank. 


if  ashes  are  permitted  to  collect  below  the  firebox,  the  fire  is 
likely  to  go  out.  What  seems  to  be  necessary  for  burning  ? 
Think  of  other  examples  of  burning  that  are  familiar  to 
you.  Does  air  always  seem  to  be  necessary?  Is  heat  or 

54 


IMPORTANCE   TO   US  OF  OXIDATION   (BURNING)         55 

light  produced  in  every  case?    The  following  experiment 
will  show  that  some  of  the  air  is  used  up  in  burning. 

Experiment.  —  Place  a  lighted  candle  on  a  cork  floating  in  a  pan  of 
water  and  invert  a  glass  jar  over  it  (Figure  51).  After  the  candle 
stops  burning,  the  water  rises  in  the  jar  to  take  the  place  of  the  air 
that  was  used  up.  The  part  of  the  air  that  is  used 
in  burning  is  called  oxygen,  and  the  uniting  of  the 
oxygen  with  the  substance  which  is  being  burned 
(fuel)  is  called  oxidation. 

Experiment.  —  To  find  out  if  -any  new  substance 
is  produced  in  burning,  burn  a  piece  of  charcoal 
(carbon)  over  the  mouth  of  a  test  tube  containing 
lime  water.  Shake  the  lime  water.  What  is  the 
result  ?  This  milky  appearance  in  the  lime  water  is  the  test  for  a  gas 
called  carbon  dioxide. 

It  is  evident,  therefore,  that  in  the  burning  of  carbon  the 
carbon  disappears  and  there  is  produced  a  new  substance 
called  carbon  dioxide,  a  gas  made  by  the  combination  of 
carbon  with  the  oxygen  of  the  air.  Experiments  have  been 
performed  which  show  that  the  weight  of  the  carbon  dioxide 
formed  is  exactly  equal  to  the  weight  of  the  carbon  which  was 
burned  plus  the  weight  of  the  oxygen  used.  This  combina- 
tion of  carbon  and  oxygen  is  accompanied  by  heat  and  light. 

A  change  in  which  a  new  kind  of  substance  is  formed  is 
called  a  chemical  change. 

Carbon  and  oxygen  are  simple  substances  which  by  no 
method  yet  discovered  have  been  separated  into  anything 
else.  Carbon  dioxide,  on  the  other  hand,  may  be  shown  to 
be  composed  of  carbon  and  oxygen  combined  in  a  definite 
proportion.  Carbon  dioxide  is  a  gas  that  will  prevent 
burning  and  is  therefore  an  entirely  different  substance 
from  its  constituents,  namely,  carbon  which  is  a  solid  and 
oxygen  which  is  necessary  for  burning. 


56 


GENERAL  SCIENCE 


Substances,  like  carbon  and  oxygen,  which  cannot  be 

separated  into  two  or  more  substances  are  called  elements. 

Some  of  the  common  elements  are  nitrogen,  hydrogen,  sul- 
phur, phosphorus,  iron,  copper, 
sodium,  potassium,  chlorine,  and 
silicon. 

Substances  like  carbon  dioxide 
are  called  compounds.  Water  is 
a  compound  composed  of  the  two 
elements,  hydrogen  and  oxygen. 
Starch  is  a  compound  of  carbon, 
hydrogen,  and  oxygen.  Lime- 
stone is  a  compound  containing 
the  elements,  calcium,  carbon, 
and  oxygen.  Almost  all  sub- 
stances we  know  of  are  compounds 
of  two  or  more  of  about  a  dozen 
elements.  Altogether  about  80 
elements  have  been  discovered, 

but  many  of  these  occur  in  very  small  quantities  or  are  not 

found  in  common  compounds. 

Explain :   (1)  The  failure  of  a  furnace  to  burn  if  ashes  are 


FIGURE  52  a. — BUNSEN  BURNER. 


FIGURE  52  b.  —  GAS  STOVE  BURNER. 


A,  gas  inlet ;  B,  air  chamber ;  F,  air  inlet ;  G,  tube  containing  mixture 
of  gas  and  air ;  C,  outlet  of  gas  mixture. 


IMPORTANCE  TO   US  OF  OXIDATION  (BURNING)        57 

not  removed ;  (2)  The  failure  of  a  wood  fire  to  burn  if  wood 
is  not  arranged  loosely;  (3)  The  reason  for  the  holes  at 
the  base  of  a  lamp  or  of  a  Bunsen  burner  (Figure  52  a) ; 
(4)  Why  firemen  have  more  difficulty  in  checking  a  big  fire 
when  wind  is  blowing  hard;  (5)  Construction  of  a  gas 
stove  burner  (Figure  52  b). 

Problem  2.    How  the  power  of  an  automobile  is  produced. 

—  We  all  know  that  gasoline  is  burned  to  give  the  engines 
of  automobiles  and  motor  boats  their  power.  That  there 


Admhalor 


Compression  Stroke 


Power  Stroke 
^     Spar 


Exhaust  Stroke 


3412 

FIGURE  53.  —  MOVEMENTS  OF  PISTON  OF  GAS  ENGINE. 

Diagram  showing  how  the  explosion  of  a  mixture  of  air  and  gasoline  vapor 
produces  movement  in  the  gasoline  engine. 

is   power    developed  in  the  burning  of  gasoline  may  be 
illustrated  by  a  very  simple  experiment. 

Experiment.  —  Make  a  hole  in  the  side  of  a  coffee  pot  or  a  can  with 
hinged  lid,  a  short  distance  from  the  bottom.     Into  the  can  pour  a 


58  GENERAL   SCIENCE 

few  drops  of  high  grade  gasoline  and  close  the  lid.  Put  a  burning 
match  or  taper  through  the  opening  at  the  side.  An  explosion  will 
occur  which  lifts  the  lid. 

In  the  gas  engine,  a  mixture  of  gasoline  vapor  and  air 
compressed  in  the  cylinder  is  exploded  by  a  spark  from  the 
spark  plug  and  the  piston  is  thrown  back  with  great  force 
(Figure  53).  By  means  of  a  crank  shaft  and  the  gears  this 
power  is  made  to  turn  the  rear  wheels  of  the  automobile 
or  the  screw  of  the  motor  boat. 

Explain  :  (1)  The  striking  back  of  a  Bunsen  burner  (Fig- 
ure 52  a)  ;  (2)  The  popping  of  a  gas  grate  or  gas  stove  when 
lighted  (Figure  52  b). 

.Problem  3.  How  a  match  is  lighted.  —  Explain  what 
you  usually  do  to  light  a  match.  Can  you  light  a  match 
without  rubbing  it  over  a  somewhat  rough  surface?  What 
do  you  think  was  the  reason  for  rubbing  the  match  over  a 
rough  surface? 

Can  you  light  a  piece  of  wood  in  the  same  way  that  the 
match  was  lighted  ? 

Compare  the  head  of  the  match  with  the  wooden  stick  as 
to  the  ease  of  starting  it  to  burn.  What  then  is  the  reason 

for  the  head  of  the  match 
(Figure  54)  ? 


-CHICTLY  OXIDIZING  MATERIAL 


starts   to    burn   at   a   much 

lower  temperature  than  wood,  it  is  said  to  have  a  lower 
kindling  temperature.  How  would  you  define  kindling 
temperature  ? 

The  head  of  the  ordinary  parlor  or  friction  match  is 
usually  a  mixture  of  (1)  phosphorus  and  a  substance  which 
readily  gives  out  oxygen,  (2)  some  ground  glass  to  increase 


IMPORTANCE   TO   US  OF  OXIDATION  (BURNING)         59 

friction,  (3)  glue,  and  (4)  coloring  matter.  The  stick  is 
dipped  into  paraffin  before  the  head  is  put  on. 

You  can  now  give  the  steps  in  the  lighting  of  a  match. 
What  does  the  rubbing  or  scratching  of  it  on  a  rough  surface 
do?  What  is  the  effect  of  the  burning  of  the  phosphorus 
upon  the  paraffin  ?  What  is  the  effect  of  the  burning  of  the 
paraffin  upon  the  wood  of  the  match  stick?  The  flame  is 
caused  by  the  burning  of  the  gases  which  are  given  off  when 
the  wood  is  highly  heated. 

Since  ordinary  friction  matches  are  a  great  source  of 
danger  from  fire,  efforts  have  been  made  to  produce  a  match 
that  is  less  dangerous.  One  method  has  been  to  coat  the 
sides  of  the  head  with  a  substance  that  has  a  relatively 
high  kindling  temperature.  The  "  birds-eye  "  matches  are  of 
this  type.  To  lessen  the  danger  from  fire,  the  "  safety  " 
match  also  has  been  invented.  You  are  all  familiar  with 
the  matches  which  will  not  usually  light  unless  scratched  upon 
a  special  striking  surface.  The  heads  of  these  matches  con- 
tain a  substance  which  gives  out  oxygen  when  heated  but 
contains  no  phosphorus,  the  phosphorus  mixture  being  in  the 
striking  surface  on  the  side  of  the  box. 

You  will  notice  that  some  match  sticks  do  not  continue 
to  burn  until  the  entire  stick  has  burned  up.  This  is  be- 
cause the  sticks  have  been  soaked  in  a  liquid  that  hinders 
burning.  Explain  the  great  value  of  this. 

Formerly  the  manufacture  of  matches  was  a  very  dan- 
gerous occupation  as  the  white  or  yellow  phosphorus  used 
poisoned  the  workers,  especially  affecting  the  jaw  bones. 
The  use  of  this  form  of  phosphorus  has  now  been  prohibited 
in  practically  all  civilized  countries,  and  either  red  phos- 
phorus or  a  compound  of  phosphorus  and  sulphur,  both  non- 
poisonous,  is  used  in  production  of  matches, 


60 


GENERAL   SCIENCE 


Explain :  (1)  The  lighting  of  a  gas  jet ;  (2)  the  starting 
and  continued  burning  of  a  coal  fire ;  (3)  The  difficulty  of 
lighting  a  match  when  the  wind  is  blowing. 

Problem  4.  What  causes  iron  to  rust.  —  This  question 
may  be  answered  by  performing  the  following  experiment. 

Experiment.  —  Put  into  a  test  tube  a  small  quantity  of  iron  filings 
and  a  few  drops  of  water.  Move  the  test  tube  around  until  the  moist 

iron  filings  form  a  layer  sticking  to  the 
inside  of  the  tube.  Place  the  test 
tube,  mouth  down,  in  a  glass  of  water. 
Note  how  much  of  the  tube  is  filled 
with  air.  Examine  again  on  the  follow- 
ing day. 

Experiment.  —  Test  the  air  that 
remains  in  the  test  tube  for  the  pres- 
ence of  oxygen.  This  may  be  done  as 
follows :  Keeping  a  finger  over  the 
bottom  of  the  test  tube  turn  it  so  that 
the  mouth  is  up.  Insert  into  the  air  in 
the  test  tube  a  lighted  splinter  or  taper. 
Does  the  taper  continue  to  burn? 
What  does  this  prove?  What,  there- 
fore, do  you  think  happens  in  the  rust- 
ing of  iron  ? 


FIGURE  55.  -RUSTING  OF  IRON. 


Can  you  suggest  a  reason  for 
not  noticing  any  heat  or  light? 

It  is  evident  that  some  cases  of  oxidation  are  relatively  slow. 
It  is  interesting  to  note  that  moisture  also  is  necessary  for 
the  rusting,  so  that  this  process  of  oxidation  is  not  quite 
so  simple  as  some  of  the  other  cases  which  have  been 
mentioned. 

In  addition  to  the  rusting  of  iron  there  are  many  other 
common  happenings  which  are  the  result  of  slow  oxidation. 


IMPORTANCE  TO   US  OF  OXIDATION  (BURNING)         61 

Rub  a  match  over  the  hand  in  the  dark.  What  do  you  ob- 
serve ?  If  paint  containing  linseed  oil  is  allowed  to  stand  a 
short  time,  a  tough  skin  is  formed  on  its  surface.  This  is 
caused  by  slow  oxidation  of  the  oil  in  the  paint.  The  same 
thing  happens  when  the  paint  is  spread  upon  a  surface.  The 
"  drying  "  of  such  paint  is  due  to  oxidation,  and  not  to  real 
drying. 

Oily  rags  which  have  been  thrown  together  in  a  heap  some- 
times catch  fire.    What  is  the  explanation  of  this  fact? 


FIGURE  56.  —  SECTIONAL  VIEW  OF  A  HOTBED. 

The  oil  slowly  oxidizes  and  the  heat  which  is  produced  grad- 
ually increases  until  the  temperature  has  been  raised  to  the 
kindling  point.  The  whole  mass  will  then  break  into  flames. 
This  is  called  spontaneous  combustion.  Why  does  oily 
clothing  not  catch  fire  spontaneously  if  hanging? 

It  is  not  an  uncommon  occurrence  in  the  country  for  a 
barn  filled  with  slightly  damp  hay  to  catch  fire.  In  this 
case  the  production  of  heat  is  probably  hastened  by  the 
action  of  small  living  plants,  called  bacteria,  which  are  present 
on  the  stems  of  the  grass  or  come  from  the  air.  The  hay 
does  not  give  off  the  heat  readily,  and  finally,  as  in  the  case  of 


62 


GENERAL   SCIENCE 


the  oily  rags,  sufficient  heat  accumulates  until  the  kindling 
point  is  reached. 

The  heat  produced  in  a  hotbed  is  formed  in  the  same  way 
as  the  heat  was  produced  in  the  hay  barn,  but  it  does  not 
reach  the  point  where  the  oxidation  becomes  rapid  enough 
to  give  off  light.  A  hotbed  is  made  of  decomposing  organic 
matter,  usually  a  mixture  of  straw  and  horse  manure. 


FIGURE  57. —  FACTORY  WRECKED  BY  A  DUST  EXPLOSION. 

This  is  covered  with  a  layer  of  soil.  The  bed  is  inclosed  with 
frames  of  glass  or  cheesecloth  to  prevent  the  escape  of  the 
heat  produced  (Figure  56).  The  hotbed  is  used  for  forcing 
the  early  growth  of  plants. 

Explosions  occur  in  poorly  ventilated  coal  bunkers  and 
flour  warehouses  (Figure  57).  How  can  you  account  for 
this?  Why  is  the  fineness  of  the  dust  particles  a  factor? 
Why  is  an  explosion  not  apt  to  occur  unless  the  ventilation 
is  poor? 


IMPORTANCE   TO   US  OF  OXIDATION   (BURNING)         63 


Problem  5.  Why  coal  is  burned.  —  Enormous  quantities 
of  coal  are  used  every  year.  A  coal  famine  is  a  very  serious 
matter.  During  the  winter  of  1917-18  many  cities  suffered 
from  shortage  of  coal.  In  many  cases  theaters,  schools, 
and  libraries  were  closed;  and  factories  were  shut  down, 
throwing  thousands  of  people  out  of  employment.  Trans- 
portation facilities  were  interrupted;  the  use  of  lights  was 
very  much  restricted,  resulting 
in  much  inconvenience  and  loss. 

In  your  own  home  or  apart- 
ment building,  coal  is  burned  for 
production  of  heat.  But  in  many 
cases,  the  production  of  heat  is 
not  the  final  result  desired.  In 
the  steam  engine,  the  heat  pro- 
duced by  the  burning  of  the  coal 
is  used  to  change  water  into 
steam  which  gives  the  engine  the 
power  to  do  many  things.  What 


B,   the   exhaustion    to   close   of 
1911;  C,  production  in  1911. 


FIGURE  58.  —  AVAILABLE  COAL 
SUPPLY. 

A,  dimensions  10  miles  along 
each  edge,  represents  the  total 
are    some    ot    the    things   which    coal  resources  of  United  States  ? 

steam  engines  can  do?  Most 
electric  power  houses  have  great 
steam  engines  which  are  used  for  the  generation  of  electricity. 
Therefore,  from  what  source  may  electrical  power  be  ob- 
tained ?  What  are  some  of  the  things  that  electricity  can  do  ? 
To  what  power,  therefore,  may  all  these  things  be  traced  ? 

It  will  thus  be  seen  that  heat,  light,  electrical  and  mechan- 
ical power  may  be  changed  one  into  another.  They  are 
different  forms  of  energy.  Energy  may  be  defined  as  the 
capacity  for  doing  work. 

Suggest  specific  examples  which  are  known  to  you  of  the 
change  of  one  form  of  energy  into  another. 


64 


GENERAL   SCIENCE 


v^ 


IMPORTANCE   TO   US  OF  OXIDATION  (BURNING)         65 

What  is  your  conclusion  as  to  why  coal  is  burned  ?  Name 
other  substances  which  are  burned  for  this  purpose.  These 
various  substances  are  called  fuels.  What  is  your,  definition 
of  a  fuel? 

Problem  6.  How  available  energy  is  supplied  to  the 
human  body.  —  How  can  the  energy  in  our  bodies  and  in 
the  bodies  of  animals  be  explained?  Every  movement  of 
our  body  demands  muscular  energy.  If  your  body  weighs 
one  hundred  pounds,  every  time  you  take  a  step  you  must 
lift  one  hundred  pounds.  Energy  is  needed  even  iPor  the 
beating  of  the  heart,  for  the  digestion  of  food,  and  for  the 
other  involuntary  activities  of  the  body. 

If  you  will  think  of  all  the  activities  of  the  body  at  work 
and  play  during  the  day,  you  may  realize  to  some  extent  the 
need  of  the  body  for  energy.  In  addition  to  this  energy, 
the  temperature  must  be  kept  at  about  98.6  degrees  Fahren- 
heit, winter  and  summer,  day  and  night,  in  spite  of  the  con- 
stant losses  of  heat  from  the  body. 

Judging  from  the  way  that  energy  is  made  available  in 
engines  and  machines,  what  do  you  suspect  to  be  the  source 
of  the  energy  of  the  human  body?  The  correctness  of 
your  answer  can  be  tested.  If  it  is  correct,  oxygen  must 
be  taken  into  the  body,  a  constant  supply  of  fuel  must  be 
furnished,  and  carbon  dioxide  must  be  given  off. 

Evidently  the  air  which  we  breathe  in  must  furnish  the 
oxygen.  Does  the  air  breathed  out  contain  an  increased 
amount  of  carbon  dioxide?  This  may  be  found  out  by  the 
following  experiment. 

Experiment.  —  Put  some  lime  water  into  a  test  tube  and  breathe 
into  it  through  a  glass  tube.  What  is  the  result  ?  You  will  remember 
that  a  milky  appearance  indicates  the  presence  of  carbon  dioxide. 
Conclusion  ? 


66 


GENERAL   SCIENCE 


Careful  analysis  shows  that  expired  air  (air  breathed  out) 
contains  about  25  per  cent  less  oxygen  than  inspired  air 
(air  breathed  in),  with  a  correspond- 
ing increase  of  carbon  dioxide. 

What  constitutes  the  fuel  in  the  body  f 
—  It  is  the  food.  Just  as  you  may 
obtain  heat  and  light  and  power  to 
run  engines  by  the  burning  of  oil,  so  in 
the  body  the  fat,  a  form  of  oil,  is 
burned  to  produce  heat  energy  and 
muscular  energy.  Light  is  not  pro- 
duced, since  the  process  goes  on  too 
slowly.  Likewise,  other  food  materials 
are  burned  in  the  body  to  produce 
energy  (Figure  60).  An  ounce  of  fat 
or  starch  burned  inside  of  the  body 
will  furnish  the  same  number  of  heat 
or  energy  units  as  if  it  were  burned 
outside  of  the  body. 

Sum  up  now  your  conclusions  as  to 
how  energy  is  made  available  in  the 
human  body.  Compare  this  process 
FIGURE  60. -FUEL  VALUE  in  the  human  body  with  what  goes 
OF  SOME  COMMON  FOODS,  on  in  the  fire  box  of  a  furnace  or 

A  calorie  is  the  amount   engine, 
of  heat  necessary  to  raise         TTT1        ,  i  •        T_      j          j 

the  temperature  of  i  kilo-  Why  does  a  man  working  hard  need 
gram  of  water  1°  centi-  more  food  than  one  who  is  not  per- 
forming hard  muscular  work? 

Why  do  we  eat  more  food  in  the  winter  than  in  the  summer  ? 

By  carefully  taking  temperatures,  it  has  been  shown  that 
the  energy  is  set  free  in  the  part  of  the  body  that  is  active ; 
chiefly  of  course  in  the  muscles. 


CALORIFS" 


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IMPORTANCE   TO   US  OF  OXIDATION  (BURNING)         67 

Why  do  the  muscles  of  the  body  which  are  used  most  not 
become  overheated?  The  circulating  blood,  is  constantly 
receiving  heat  from  the  more  active  parts  of  the  body,  and 
is  giving  it  to  those  parts  which  are  less  active.  As  a  result, 
the  temperature  of  the  body  is  equalized.  Since  the  heat 
energy  and  muscular  energy  are  made  available  in  the  various 
parts  of  the  body,  three  other  uses  of  the  circulating  blood 
are  indicated.  What  are  they? 

Problem  7.  Do  plants  breathe?  —  If  they  do,  then  there 
must  be  some  proof  that  three  different  things  occur.  What 
are  they? 

To  find  out  if  plants  use  oxygen  and  give  out  carbon 
dioxide  perform  the  following  experiment. 

Experiment.  —  Into  each  of  two  flasks  put  an  equal  number  of 
peas  that  have  been  soaked  in  water.  Cork  one  flask  so  that  no  air 
can  pass  into  it  or  out  of  it.  Allow  the  other  flask  to  remain  open. 
Place  the  flasks  side  by  side  so  that  they  will  have  the  same  conditions 
of  light  and  heat.  At  the  end  of  a  week  observe  the  contents  of  the 
flasks. 

What  has  happened  ?  What  does  this  prove  ?  A  blazing 
splinter  passed  into  the  open  flask  continues  to  burn.  What 
happens  when  it  is  passed  into  the  flask  which  has  been  kept 
closed  ?  What  does  this  prove  ?  If  the  air  in  each  flask  is 
tested  for  the  presence  of  carbon  dioxide,  it  will  be  found 
that  the  closed  flask  contains  a  considerable  amount  of 
carbon  dioxide  while  the  other  does  not  contain  an  appre- 
ciable quantity.  What  does  this  prove?  What  is  your 
general  conclusion  as  to  the  use  of  oxygen  by  sprouting 
seeds  ? 

If  oxidation  goes  on  in  sprouting  seeds  we  should  expect 
that  heat  and  energy  of  movement  would  result. 


68 


GENERAL   SCIENCE 


Experiment.  —  Into  a  flask  put  an  inch  or  more  of  pea  seeds  which 
have  been  killed  by  being  heated  for  a  short  time  in  an  oven.  Into 
another  flask  put  an  equal  amount  of  living  pea  seeds.  Put  into  each 
flask  the  same  amount  of  moisture.  Place  a  thermometer  in  each  flask, 
covering  the  mercury  bulb  with  the  peas.  Permit  free  access  of  air. 
From  time  to  time  note  whether  the  thermometers  register  a  difference 
in  temperature. 

It  will  be  found  that  heat  is  generated  by  the  sprouting 
pea  seeds.  What  observations  have  you  made  that  will 


FIGURE  61.  —  FLOODED  REGION. 
Trees  killed  by  having  their  roots  drowned. 

show  that  sprouting  seeds  are  able  to  lift  a  weight  or  in 
other  ways  exert  mechanical  energy  ? 

Seedlings  take  in  the  oxygen  of  the  air  and  give  off  carbon 
dioxide  through  any  part  of  their  surfaces.  In  fully  grown 
plants  this  occurs  chiefly  through  the  young  roots  and  leaves. 
In  a  region  flooded  for  a  considerable  time,  the  trees  will 


IMPORTANCE  TO   US  OF  OXIDATION  (BURNING)         69 

die,  chiefly  because  their  roots  have  been  unable  to  get 
oxygen  from  the  air  (Figure  61).    They  have  been  drowned. 

Problem  8.  How  animals  take  in  oxygen  and  give  off 
carbon  dioxide.  —  Animals  have  various  ways  of  taking 
in  oxygen  and  giving  off  carbon  dioxide. 

(a)  Very  simple  animals.  —  Earthworms  and  other 
simple  animals  have  no  lungs.  How  then  do  you  suppose 
they  can  take  in  oxygen?  Plants,  we  already  know,  breathe 


Pharynx  Muscles 
Brain    ^_A-^~^-^-^-_ ^__  Stomach- Intestine 


Oesophagus        .Bloodvessels 


FIGURE  62. —  ORGANS  OF  AN  EARTHWORM. 

Many  small  blood  vessels  (not  represented  in  the  figure)  pass  from  near  the 
surface  of  the  body  into  the  large  vessels,  which  are  also  near  the  surface. 

through  thin  moist  membranes.  Possibly  this  is  true  of  the 
earthworm.  If  so,  the  earthworm  must  have  a  thin  moist 
skin.  Examine  an  earthworm  to  see  if  this  is  the  case. 
An  earthworm  dies  as  soon  as  its  skin  becomes  dry.  Fre- 
quently after  a  rain,  many  earthworms  come  to  the  surface 
because  their  burrows  have  become  filled  with  water.  Early 
in  the  morning  they  may  be  seen  crawling  on  the  sidewalk, 
but  it  will  be  noticed  that  they  die  as  soon  as  the  sun  has 
dried  their  bodies. 

If  an  earthworm  breathes  through  its  skin,  what  should 
be  directly  below  the  thin  moist  membrane  of  the  skin? 


70  GENERAL   SCIENCE 

Sum  up  your  conclusions  as  to  how  the  earthworm  takes 
oxygen  into  its  body  and  gives  out  the  carbon  dioxide. 

(6)  Insects  cannot  breathe  through  the  skin.  Why  not? 
If  a  grasshopper  is  watched,  it  will  be  noticed  that  the 
hinder  portion  of  the  body  (abdomen),  which  is  made  up  of 
rings,  expands  and  contracts  in  a  way  similar  to  the  expansion 
and  contraction  of  our  own  chests  during  breathing.  These 
movements  of  the  grasshopper  are  breathing  movements. 

The  air  containing  oxygen  goes  into  the  body  with  each 
expansion,  and  the  air  containing  carbon  dioxide  passes 
out  at  each  contraction.  Where  does  the  air  go  in?  If 
you  look  very  carefully  along  each  side  of  the  body  you  will 
see  a  number  of  small  holes,  one  in  each  of  the  divisions  of 
the  abdomen.  There  are  also  two  pairs  of  holes  in  the  thorax, 
the  part  of  the  body  to  which  the  legs  and  wings  are  attached. 
Connected  with  these  openings  are  small  branching  tubes 
which  carry  air  to  all  parts  of  the  body.  , 

These  breathing  pores  can  usually  be  seen  very  distinctly 
on  the  sides  of  a  beetle  larva  (Figure  63)  or  of  a  caterpillar, 
which  you  know,  of  course,  is  the  young  of  a  moth  or 
butterfly.  The  young  or  larva  of  the  mosquito  which  lives 
in  water  has  only  one  breathing  pore,  which  is  located  at 
the  tail  end  of  the  body.  In  order  to  get  air,  it  must  come 
to  the  surface  hanging  head  .downward. 

Mosquitoes,  therefore,  may  be  destroyed  by  pouring 
oil  on  ponds  in  which  they  live.  The  oil  spreads  over  the 
surface  of  the  water,  forming  a  thin  layer  through  which 
air  will  not  pass.  Thus  the  mosquito  larvae  are  unable  to 
obtain  air  when  they  come  to  the  surface,  and  suffocate. 

(c)  Fish  breathe  by  means  of  gills  which  are  located  under 
flaps  just  back  of  the  head.  If  you  examine  a  fish  which 
has  been  sent  from  the  market  with  the  head  still  attached, 


IMPORTANCE   TO   US  OF  OXIDATION  (BURNING)         71 


you  will  see  under  these  flaps  (opercula)  four  bony  arches 
on  each  side.  Between  these  arches  are  slits  opening  into 
the  back  of  the  mouth.  Each  arch  has  upon  its  outer  edge 
a  large  number  of  small,  reddish,  threadlike  structures, 
(gill-filaments)  which  project  backward  from  the  arch. 
The  inner  side  of  each  arch  has  on  it  a  number  of  hard, 
pointed  structures  (gill-rakers)  (Figure  64). 


if^ 


FIGURE  63. — STAGES  IN  THE  LIFE  HISTORY  OF  A  BEETLE. 
Note  the  breathing  pores  on  the  side  of  the  larva  (the  worm-like  stage). 

Observe  a  fish  in  an  aquarium.  Do  you  notice  any  move- 
ments which  are  probably  connected  with  breathing  ?  Water 
passes  into  the  mouth  of  the  fish  and  out  through  the  gill 
slits  at  the  side  of  the  head.  Suggest  a  use  for  the  gill 
rakers.  The  heart  is  located  on  the  under  side  of  the  fish, 
in  the  space  between  the  back  parts  of  the  gills.  It  pumps 
the  blood  forward  through  a  vessel  which  has  four  branches 
on  each  side,  one  to  each  gill  arch.  These  vessels  in  turn 
send  off  very  small  vessels  into  the  gill  filaments. 

What  do  you  suppose  the  blood  in  these  vessels  receives  ? 


72 


GENERAL   SCIENCE 


What  does  it  give  off?  The  blood  from  the  gill  filaments 
passes  into  vessels  which  carry  it  to  the  upper  part  of  the 
gill  arches  and  from  there  it  passes  to  all  parts  of  the  body, 
finally  returning  to  the  heart  loaded  with  carbon  dioxide  and 
without  its  oxygen.  What  has  become  of  the  oxygen? 
What  is  the  source  of  the  carbon  dioxide  ? 


.Gill    Filaments. 


Gill  Rakers 


Gill  of  tile  Fish 


Gfil  of  White  Fish 


FIGURE  64.  —  BREATHING  ORGANS  OF  FISH. 

(d)  Higher  animals.  —  Most  animals  that  live  in  the  air, 
except  insects,  breathe  by  means  of  lungs  which  are  really 
thin-walled  bags  connected  with  the  outside  air  through 
the  nostrils.  The  walls  of  the  lungs  contain  many  small 
blood  vessels  (capillaries).  The  blood  in  these  takes  in 
oxygen  and  gives  off  carbon  dioxide. 


IMPORTANCE   TO    US  OF  OXIDATION  (BURNING)         73 

INDIVIDUAL  PROJECTS 

1.  Production  of  pure  oxygen  and  comparison  of  the  burning  of 
substances  in  air  and  in  oxygen. 

2.  Making  a  safety  match. 

3.  Demonstration  of  how  the  explosion  of  gasoline  causes  the  gas 
engine  to  work. 

4.  Demonstration  of  how  air  and  gas  are  mixed  in  a  gas  stove. 

5.  Construction  and  use  of  a  hotbed. 

6.  Making  gas  from  coal  and  wood. 

7.  Collection  of  various  kinds  of  coal.     Source  and  special  use  of 
each  kind. 

8.  Dissection  of  the  blood  system  and  breathing  system  of  a  fish. 

REPORTS 

1.  History  of  the  discovery  of  oxygen. 

2.  The  coal  regions  of  the  United  States,  methods  01  mining,  and 
approximate  number  of  years  our  supply  will  last. 

3.  Formation  of  coal. 

4.  Different  ways  in  which  animals  breathe. 

REFERENCES  FOR  PROJECT  VI 

1.  Book  of  Wonders,  Bodmer,  R.     (Fire.) 

2.  Chemical  History  of  a  Candle,  M.  Faraday.     Harper  &  Bros. 

3.  Fuels  of  the  Household,  Marian  White.     Whitcomb  &  Barrows, 
Boston. 

4.  Sweden  and  Safety  Matches,  N.  B.  Allen.     Ginn  &  Co. 

5.  Diggers  in  the  Earth,  E.  M.  Tappan.     Houghton  Mifflin  Co. 
(Coal  mining.) 

6.  Earth   and   Sky  Every   Child   Should  Know,   J.   E.   Rogers. 
Doubleday,  Page  &  Co. 

7.  The  United  States,  J.  O.  Winston.    D.  C.  Heath.     (Coal.) 

8.  The  Story  of  Oil,  W.  S.  Tower.     D.  Appleton  &  Co. 

9.  Field  and  Forest  Handy  Book,  Beard.     Scribners.    (Camp  cook- 
ing and  stoves.) 

10.   American  Inventions  and  Inventors,  Mowry,     Silver*  Burdett 
&  Co.     (Fire,  Fuel,  Matches.) 


PROJECT  VII 

PREVENTION   OF  DESTRUCTIVE  BURNING   OR 
OXIDATION 

WE  have  seen  that  oxidation  is  very  valuable  in  giving  us 
usable  energy.  Can  you  name  examples  of  oxidation  or 
burning  which  are  harmful?  From  what  we  have  learned 


FIGURE  65.  —  RESULTS  OF  A  FOREST  FIRE. 

Not  only  have  the  trees  been  destroyed  but  almost  all  the  vegetable 
matter  (humus)  of  the  soil  has  been  burned  away. 

about  burning,  we  should  be  able  to  suggest  means  by 
which  destructive  oxidation  may  be  prevented. 

What  two  conditions  are  always  necessary  for  oxidation? 
Suggest  another  which  is  usually  necessary.  It  is  clear  that 
if  any  one  of  the  necessary  conditions  is  removed,  then 

74 


PREVENTION  OF  DESTRUCTIVE  BURNING  OR  OXIDATION     75 

burning  or  oxidation  must  stop.  Our  problem  then  is  simply 
to  discover  methods  by  which  these  conditions  necessary 
for  oxidation  may  be  prevented. 

Problem  1.  How  destructive  oxidation  may  be  pre- 
vented by  excluding  the  air. —  (a)  Coating  iron  with  a  sub- 
stance which  does  not  rust.  What  are  some  of  the  ways 
in  which  air  may  be  kept  from  substances  which  are  apt 
to  undergo  harmful  oxidation?  How  are  iron  fire  escapes 
kept  from  rusting?  Give  other  examples  of  the  use  of  this 
means. 

Is  a  tin  pan  made  entirely  of  tin?  Give  proof  for  your 
answer.  Tinware  is  made  of  thin  sheets  of  iron  which, 
after  having  been  thoroughly  cleaned,  are  dipped  into  melted 
tin.  Iron  also  may  be  prevented  from  rusting  by  covering 
it  with  a  layer  of  zinc,  applied  in  the  same  way.  This  is 
called  galvanized  iron  and  is  very  generally  used  for  pails, 
water  troughs,  and  similar  articles.  It  is  not  used  for  cook- 
ing utensils,  as  zinc  may  form  poisonous  compounds. 

How  is  the  iron  hot  water  boiler  in  the  kitchen  prevented 
from  rusting  ?  It  is  usually  painted  with  a  volatile  substance 
(a  substance  which  evaporates  quickly)  in  which  there  is 
powdered  aluminum,  a  metal  which  is  not  affected  by  the  air. 
The  volatile  liquid  disappears,  leaving  on  the  boiler  a  thin 
layer  of  powdered  aluminum  which  not  only  gives  the  boiler 
a  pleasing  appearance  but  also  prevents  it  from  rusting. 

Iron  may  also  be  prevented  from  rusting  by  covering  it 
with  a  layer  of  nickel,  which  is  put  on  by  the  use  of  elec- 
tricity (nickel  plating). 

The  iron  of  stove  pipes  and  locomotive  boilers  is  usually 
protected  from  rusting  by  a  coating  which  is  produced  by 
passing  over  the  hot  iron  a  mixture  of  highly  heated  steam 


76 


GENERAL   SCIENCE 


and  carbon  dioxide.  This  coating  is  an  oxide  of  iron,  dif- 
ferent from  the  ordinary  oxide  of  iron,  and  it  protects  the 
iron  from  further  oxidation.  Iron,  coated  in  this  way,  is 
called  Russia  iron. 

(b)  How  do  .fire  extinguishers  work  f  —  A  fire  is  put  out  by 
surrounding  the  burning  material  with  a  gas  which  will 

not  burn.  What  happens 
then  to  the  fire?  Some 
fire  extinguishers  contain 
a  liquid,  carbon  tetrachlo-. 
ride,  which  becomes  a  non- 
inflammable  gas  when  it 
is  squirted  on  the  fire. 
In  the  fire  extinguishers 
which  are  inverted  just 
before  being  used,  sul- 
phuric acid  falls  into  a 
solution  of  soda  (Figure 
66).  The  action  of  the 
acid  upon  the  soda  pro- 
duces a  large  quantity  of 

carbon  dioxide  which  forces  out  the  mixture  of  water  and 

carbon  dioxide.     What  effect  will   this  have  when  played 

upon  the  burning  objects? 

Explain  the  reason  for  keeping  pails  of  sand  in  various 

parts  of  a  garage.     Why  is  water  not  used  for  the  purpose? 

Will  water  mix  with  gasoline? 

(c)  Smothering  a  fire.  —  Explain  why  it  is  advisable  to 
roll  a  person  whose  clothing  is  on  fire  in  a  rug  or  blanket. 
Is  it  advisable  for  a  person  to  start  to  run  if  his  clothing 
is  on  fire  ?     WThy  ?     Why  are  burning  draperies  pulled  down 
and  stamped  upon? 


FIGURE  66. —  FIRE  EXTINGUISHER. 


PREVENTION  OF  DESTRUCTIVE  BURNING  OR  OXIDATION     77 


Problem  2.  How  destructive  oxidation  may  be  pre- 
vented by  reducing  the  temperature  below  the  kindling 
point.  —  Throwing  water  on  a  fire,  you  all  know,  is  the 
usual  way  of  putting  it  out.  Why  do  you  suppose  it  is  so 
effective?  Do  you  think  that  the  amount  thrown  by  the 
firemen  upon  a  big  fire 
will  prevent  the  air  get- 
ting to  the  fire?  Why, 
then,  is  water  so  valu- 
able for  putting  out  a 
fire?  Reference  to  your 
study  of  ventilation  will 
help  to  answer  this  ques- 
tion. What  was  the 
effect  of  evaporation  of 
moisture  on  the  skin? 
What  becomes  of  the 
water  that  is  thrown  on 
the  fire?  What  effect 
will  this  have  upon  the 
temperature  ?  A  wet 

piece   of   wood    does   not    FIGURE  67.- FIGHTING  A  FIRE  WITH  WATER. 
burn  readily  because  the 

heat  applied  is  used  in  evaporating  the  water  instead  of 
raising  the  wood  to  its  kindling  temperature. 

Sum  up  your  conclusions  as  to  the  importance  of  water 
in  lowering  the  temperature  of  a  burning  substance  below 
the  kindling  temperature.  Do  not  forget  that  the  water  and 
steam  produced  are  also  useful  in  preventing  the  access  of  air. 


Problem   3.     How   destructive    oxidation   may   be   pre- 
vented by  removal  of  fuel  material.  —  No  fire  can  start  or 


78 


GENERAL   SCIENCE 


continue  to  burn  unless  there  is  a  supply  of  fuel  material ; 
hence,  the  inspectors  of  the  fire  department  prohibit  the 
collection  of  rubbish  in  basements  and  area  ways.  Every 
year  forest  fires  destroy  property  worth  hundreds  of  thou- 
sands of  dollars  .and  cause  the  death  of  many  people.  Prob- 
ably the  most  common  cause  of  these  fires  is  the  careless- 
ness of  campers  in  failing  to  put  out  their  camp  fires.  Very 


FIGURE  68.  —  A  FOREST  FIRE  FIGHTER. 

strict  regulations  concerning  the  use  of  fire  are  enforced 
to  prevent  the  starting  of  forest  fires.  To  limit  the  spread 
of  a  fire  if  once  started  in  a  forest  reservation,  there  are 
fire  lanes  which  are  kept  cleared  of  underbrush.  Why  do 
the  fire  lanes  stop  the  fire  ? 

Ground  fires  which  creep  along  the  ground,  depending  for 
fuel  upon  the  underbrush  and  vegetable  matter  accumu- 


PREVENTION  OF  DESTRUCTIVE  BURNING  OR  OXIDATION    79 


lated  during  many  years,  are  frequently  stopped  by  plowing 
up  a  strip  of  land  in  the  path  of  the  fire.  What  is  the 
advantage  of  this? 

During  severe  fires  in  cities 
which  threaten  to  destroy 
property  in  great  areas,  build- 
ings are  often  deliberately  de- 
stroyed by  dynamite.  What 
is  the  reason  for  this  ?  Where 
there  are  buildings  in  solid 
blocks,  fireproof  walls  are  con- 
structed at  intervals  which 
are  known  as  fire  walls. 

WThat  is  meant  by  fireproof 
construction  of  buildings  ? 
In  what  respect  is  your  school 
building  of  fireproof  construc- 
tion? In  other  buildings 
with  which  you  are  familiar, 
what  means  have  been  taken 
to  make  them  fireproof? 
What  substances  may  be  used 
in  fireproof  construction?  • 

INDIVIDUAL  PROJECTS 

1.  Make   and   demonstrate   a 
fire  extinguisher. 

2.  Collection   and   demonstra- 
tion of  fireproofing  materials. 


REPORTS 

1.  Fighting  a  forest  fire. 

2.  Fireproof     construction    of 
buildings. 


FIGURE  69.  —  FOREST  RANGER  ON 
LOOKOUT  FOR  SIGNS  OF  FOREST 
FIRES. 

If  signs  of  fire  are  discovered,  the 
ranger  telephones  to  the  fire  station 
nearest  the  fire,  indicating  by  refer- 
ence to  the  forest  map  the  exact 
location  of  the  observed  smoke. 


PROJECT  VIII 

IMPORTANCE  TO   US   OF  THE   OTHER   GASES   OF 
THE  AIR 

WE  have  seen  that  the  oxygen  of  the  air  is  of  very  great 
importance  to  us.  Mention  several  ways  in  which  it  is  of 
great  value  and  several  in  which  it  is  harmful.  The  ques- 
tion naturally  arises,  are  there  other  gases  in  the  air  and  if 
so,  of  what  importance  are  they  to  us.  The  first  problem 
therefore  is : 

Problem  1.    Does  air  contain  any  gas  besides  oxygen  ? 

Experiments.  —  (1)  Burn  a  taper  in  air,  and  then  in  oxygen. 

(2)  Burn  in  oxygen  a  bundle  of  fine  iron  wire,  dipped  in  sulphur. 
What  are  the  results?     What  is  the  conclusion? 

(3)  Expose  a  vessel  of  limewater  to  the  air.     Note  that  a  scum 
appears  on  the  surface.    This  is  an  indication  of  the  presence  of  carbon 
dioxide. 

Problem  2.    How  much  of  the  air  is  oxygen  ?  —  Can 

you  suggest  a  method  by -which  this  may  be  found  out? 

Experiment.  —  On  a  metal  disk  on  a  flat  piece  of  cork,  place  a  bit 
of  yellow  phosphorus.  Place  the  cork  -  on  water  and  invert  over  it 
a  glass  cylinder.  Examine  after  two  days.  Result?  Conclusion? 

Quantitative  experiments  have  shown  that  air  has  the 
following  composition : 
Oxygen,  20+  per  cent. 

Nitrogen,  including  several  inert  gases,  79+  per  cent. 
Carbon  dioxide,  .03  to  .04  of  1  per  cent. 

80 


IMPORTANCE  TO  US  OF  THE  OTHER  GASES  OF  THE  AIR     81 

Problem  3.     Importance  of  nitrogen  in  the  air. 

Experiment.  —  Manufacture  some  oxygen.  This  can  be  done  by 
heating  a  mixture  of  potassium  chlorate  with  manganese  dioxide  in 
a  flask.  The  gas  can  be  collected  in  a  bottle  in  the  manner  shown  in 
the  diagram  (Figure  70).  Burn  various  substances  as  wood  splinters, 
a  candle,  some  sulphur,  and  an  iron  wire  in  bottles  of  pure  oxygen. 


D 


FIGURE  70.  —  PREPARATION  OF  OXYGEN. 

A,  bunsen  burner;  B,  tube  containing  potassium  chlorate  and  manganese 
dioxide  ;  C,  vessel  containing  water  ;  D,  D,  bottles  for  collecting  gas. 

Pass  oxygen  into  a  bottle  until  it  is  one  fifth  filled.  Fill  the  remainder 
with  nitrogen,  which  may  be  made  by  heating  together  in  a  flask  the 
two  chemicals,  ammonium  chloride  and  sodium  nitrate.  Try  to  burn 
in  this  mixture  of  oxygen  and  nitrogen  a  splinter  of  wood,  a  candle,  some 
sulphur,  and  an  iron  wire.  Do  these  substances  burn  the  same  as  when 
burned  in  the  pure  oxygen? 

What  would  happen  if  the  air  contained  a  much  larger 
percentage  of  oxygen?  What  do  you  consider  to  be  the 
value  of  nitrogen  in  the  air?  Nitrogen  is  a  very  inactive 
substance.  It  is  due  to  this  property  that  nitrogen  is  an 


82  GENERAL   SCIENCE 

important  element  in  explosives.  Explain.  Under  certain 
conditions  some  of  the  nitrogen  of  the  air  may  be  used  in 
the  growth  of  plants  or  may  be  made  into  substances  from 
which  explosives  may  be  manufactured.  These  cases  will 
be  considered  later.  x 

Problem  4.  Importance  of  carbon  dioxide  of  the  air.  — 
We  found  that  certain  animals  in  breathing  give  carbon 
dioxide  to  the  air.  Also  that  it  is  added  to  the  air  in  the 
burning  of  a  candle.  In  the  same  way  it  is  given  off  in  the 
burning  of  coal,  wood,  oil,  etc.  As  a  result  what  do  you 
think  should  happen  to  the  amount  of  carbon  dioxide  in  the 
air?  But  an  examination  of  the  air  year  after  year  indi- 
cates that  there  is  no  increase  in  the  amount  of  this  gas. 
What  do  you  conclude  from  this? 

Another  interesting  fact  gained  from  the  examination 
of  the  air  is  that  the  oxygen  of  the  air  does  not  decrease  in 
quantity.  In  the  solution  of  our  problem,  therefore,  a  num- 
ber of  smaller  problems  must  be  solved.  The  first  of  these 
will  be  indicated  by  a  fact  that  is  familiar  to  you.  Wrhat 
is  the  appearance  of  partially  burned  plant  material  ?  What 
does  this  indicate  ?  Since  plants  can  grow  in  soil  which  con- 
tains no  carbon,  what  will  you  suspect  is  the  source  of  the 
carbon  ? 

Sub-problem  I.  Proof  that  carbon  compounds  are  made 
in  leaves  of  plants.  —  One  of  the  most  common  plant  sub- 
stances containing  carbon  is  starch.  There  is  no  starch  in 
the  soil  or  in  the  air,  therefore  it  evidently  must  be  made 
within  the  plant. 

•  Experiment. —--To  prove  that  starch  is  manufactured  in  a  leaf 
place  a  geranium  in  a  dark  closet  for  twenty-four  hours,  then  remove  a 
leaf  and  test  for  starch.  This  is  done  by  first  removing  the  green  col- 


IMPORTANCE  TO  US  OF  THE  OTHER  GASES  OF  THE  AIR     83 


oring  matter,  by  soaking  the  leaf  in  alcohol,  and  then  adding  iodine, 
which  gives  a  blue  color  if  starch  is  present.  What  is  the  result? 
After  this  leaf  has  been  removed,  set  the  entire  plant  in  the  sunlight, 
first  placing  upon  several  leaves  pieces  of  black  cloth  or  thin  strips  of 
cork  which  completely  exclude 
the  light  from  the  portions  of 
the  leaves  covered.  After  a 
few  hours,  remove  and  test 
several  leaves  for  the  presence 
of  starch.  What  is  the  result  ? 
What  two  things  are  proved 
by  this  experiment  ? 


Sub-problem  II.  What 
raw  materials  are  used  by 
leaves  in  making  starch? 
—  Analysis  shows  that 
starch  is  made  of  the 
following  fundamental 
substances  or  elements : 
Carbon,  6  parts;  hydro- 
gen, 10  parts;  oxygen,  5 
parts.  This  is  conven- 
iently written,  C6Hi0O5. 
Water,  which  is  made  of 
two  parts  of  hydrogen  and 
one  part  of  oxygen  (H2O), 


FIGURE  71. —  POTATO  PLANT. 


and  carbon   dioxide,  com-    A  plant  in  which  a  large  amount  of  starch 

is  stored  in  an  underground  stem.     , 
posed  of  one  part  of  carbon 

and  two  parts  of  oxygen  (CO2),  both  of  which  are  accessible 
to  the  leaf,  'contain  the  elements  necessajy  for  the  formation 
of  starch.  I(  they  were  combined,  the  result  might  be  repre- 
sented as  follows:  Carbon  dioxide  (CO2)+  Water  (H2O)  = 
Starch  (CcHioOs).  It  will  be  noted  that  to  get  sufficient 


84  GENERAL  SCIENCE 

carbon  for  the  starch,  it  is  necessary  that  six  parts  of  carbon 
dioxide  enter  into  the  combination;  and  to  provide  the 
proper  proportion  of  hydrogen,  five  parts  of  water  must 
combine  with  the  carbon  dioxide.  The  action  may  then  be 
represented  as  follows:  Six  parts  of  carbon  dioxide  might 
combine  with  five  parts  of  water  to  form  one  part  of  starch 
or 

6C02+5H20=C6H1005 

But  if  six  parts  of  CO2  unite  with  five  parts  of  H2O  to  form 
starch  (CeHioC^),  it  will  be  noticed  there  is  an  excess  of 
oxygen,  so  that  the  action  will  finally  be  represented  as 
follows : 

6  CO2+5  H2O  =  C6H10O5+6  O2 

If  in  the  leaf,  therefore,  carbon  dioxide  and  water  actually 
do  unite  in  forming  starch,  oxygen  should  be  given  off.  Does 
this  occur  ? 

Sub-problem  III.  Do  plants  give  off  oxygen  in  making 
starch  ? 

Experiment.  —  Place  some  aquarjum  plants  under  a  funnel  in  a  jar 
of  water.  Over  the  neck  of  the  funnel  put  an  inverted  test  tube  filled 
with  water.  Place  the  jar  in  the  sunlight.  What  do  you  observe  ? 

Remove  the  test  tube  without  allowing  any  of  the  contained  gas  to 
escape,  and  pass  into  the  mouth  of  the  test  tube  a  glowing  ember. 
What  happens  ?  What  does  this  prove  ? 

The  work  that  the  green  leaf  does  with  the  assistance 
of  sunlight  in  combining  carbon  dioxide  and  water  into 
starch  is  called  photosynthesis  (from  two  Greek  words : 
photo,  light,  and  synthesis,  putting  together).  .  . 

Sub-problem  IV.  Proof  that  plants  use  carbon  dioxide 
in  making  starch.  —  The  fact  that  oxygen  is  given  off  by 
plants  is  an  indication  that  carbon  dioxide  and  water  are 


IMPORTANCE  TO  US  OF  THE  OTHER  GASES  OF  THE  AIR     85 

used  by  the  plant  in  making  starch.  It  can  easily  be  proved 
by  the  following  experiment  that  carbon  dioxide  is  used  by 
plants  during  the  process  of  starch-making. 

Experiment.  —  Pass  into  a  jar  sufficient  carbon  dioxide  to  replace  the 
air  almost  entirely.  Put  into  the  jar  a  green  plant  which  has  been  kept 
in  the  dark  for  twenty-four  hours.  Pass  a  lighted  taper  into  the  jar. 
What  is  the  result?  Also  pass  into  the  jar  a  glass  rod  from  which  is 
hanging  a  drop  of  Jimewater.  What  is  the  result?  Cover  the  jar 
tightly  and  place  it  where  it  will  be  exposed  to  sunlight.  After  several 
days  again  test  the  contained  air  with  the  limewater  and  the  lighted 
taper.  Results  ?  Conclusions  ? 

Sub-problem  V.  Amount  of  carbon  dioxide  removed  from 
the  air  in  making  starch  and  wood.  —  The  woody  sub- 
stance of  plants  (cellulose)  is  also  made  of  carbon,  hydro- 
gen, and  oxygen  in  the  same  proportion  as  in  starch.  Wood, 
therefore,  represents  a  certain  amount  of  carbon  dioxide 
takerf'out  of  the  air  and  combined  with  water.  It  has  been 
calculated  that  for  every  pound  of  starch  or  cellulose  (wood 
manufactured  by  a  plant)  1.6  pounds  of  carbon  dioxide  are 
needed.  From  an  acre  of  ground  several  tons  of  dry  hay  may 
be  obtained.  A  large  proportion  of  the  dry  hay  is  cellulose, 
or  material  of  a  similar  composition.  Considering  this 
fact,  calculate  approximately  how  much  carbon  dioxide 
will  have  been  taken  from  the  air  by  a  ten-acre  field  of  hay 
during  one  season. 

The  coal  which  we  burn  has  had  a  similar  origin.  It  was 
formed  from  many  generations  of  plants  which  formed  layer 
after  layer  of  vegetable  matter.  This  was  partially  oxidized 
and  then  was  covered  by  sediment  which  finally  became 
formed  into  rock.  Soft  or  bituminous  coal  clearly  shows 
the  layers  of  vegetable  matter  of  which  it  is  composed. 

Soft  or  bituminous  coal  occurs  in  great  beds  usually  more 


86  GENERAL   SCIENCE 

or  less  horizontal  (Figure  72).  Anthracite  or  hard  coal 
is  found  in  portions  of  the  country  where  the  strata  or 
layers  of  the  rock  have  been  very  much  crumpled.  This 
crumpling  process  has  evidently  been  accompanied  by  a 
high  temperature  which  has  driven  from  the  accumulated 
vegetable  matter  many  compounds,  leaving  almost  pure 
carbon. 

Just  as  we  have  found  that  the  starch  is  made  by  plants, 
only  under  the  action  of  the  energy  of  sunlight,  so  likewise 


FIGURE  72.  —  COAL  BED. 
Horizontal  bed  of  coal  exposed  along  a  river  bed  in  Wyoming. 

in  the  cases  of  wood  and  coal  the  energy  of  the  sun  has  been 
necessary.  What,  therefore,  may  be  considered  to  be  the 
final  source  of  the  energy  given  out  in  the  process  of  the 
burning  of  wood  or  coal  ?  The  amount  of  heat  procured  by 
burning  a  piece  of  coal  may  be  considered  to  be  a  measure 
of  the  amount  of  the  sun's  energy  necessary  to  separate  the 
carbon  from  the  oxygen  of  carbon  dioxide  in  the  process  of 
photosynthesis  (Figure  73). 


IMPORTANCE  TO  US  OF  THE  OTHER  GASES  OF  THE  AIR  87 


We  are  now  able  to  understand  why  the  relative  quan- 
tities of  oxygen  and  carbon  dioxide  in  the  air  remain  the 
same  year  after  year. 


BITUMINOUS  ANTHRACITE 

COAL  COAL 


5     t      CALORIES 
PER  GRAM 


8009 


7000 


4090 


10 


5000 


4000 


3000 


2000 


1000 


FIGURE  73. —  HEATING  VALUE  OF  SOME  COMMON  FUELS. 
Note  the  relative  amounts  of  carbon  (C)  in  the  various  fuels.  What 
is  the  source  of  this  carbon  ?  What  is  the  source  of  the  hydrogen  (H)  ? 
The  calories  given  here  are  small  calories.  The  amount  of  heat  necessary 
to  raise  the  temperature  of  one  gram  of  water  1°  C-  is  one  calorie.  Fuel 
value  of  foods  is  usually  given  in  large  calories,  1000  times  greater  than 
small  calories. 


88 


GENERAL  SCIENCE 


What  are  the  chief  ways  in  which  oxygen  is  removed  from 
the  air? 

How  is  it  restored  to  the  air? 

How  do  you  suppose  the  composition  of  the  air  before  the 
carboniferous  period  (the  period  when  most  coal  was  formed) 
differed  from  the  composition  of  the  air  now  ? 


FIGURE  74. —  OIL  WELLS  IN  OKLAHOMA. 

These  wells  tap  oil  deposit  2000  to  3000  feet  below  the  surface.  Since 
petroleum  has  evidently  been  formed  from  plant  and  animal  material,  what 
is  the  source  of  its  energy  ? 

Almost  all  plants  are  green.  Is  there  any  connection 
between  the  possession  of  this  green  coloring  matter 
(chlorophyll)  and  the  ability  to  make  starch  ? 

Sub-problem  VI.  Is  the  green  coloring  matter  (chlo- 
rophyll) necessary  for  making  starch.  —  Place  a  plant 
whose  leaves  have  white  streaks  or  spots  (Tradescantia  is  a 
good  plant  to  use)  in  the  sunlight  for  several  hours.  Test 


IMPORTANCE  TO  US  OF  THE  OTHER  GASES  OF  THE  AIR     89 


the  leaves  for  starch.  Result?  Conclusion?  Experiments 
might,  also  be  performed  which  show  that  it  is  only  the 
living  leaf  that  will  manufacture  starch. 

Sub-problem  VII.  How  fish  live  in  a  balanced  aquarium.  — 
Fish  and  other  animals  may  be  kept  for  long  periods  of 
time  without  being  fed  if  they  are  in  aquaria  containing 
green  plants.  In  such 
aquaria  the  green 
plants  do  not  decrease 
in  quantity.  These 
aquaria  are  known  as 
balanced  aquaria 
(Figure  75). 

(a)  Breathing.  — 
From  what  you  have 
already    learned,    ex- 
plain how  the  fish  get 
a  supply  of  oxygen. 
What    do    you    sup- 
pose becomes  of  the 
carbon    dioxide    pro- 
duced ? 

(b)  Food  Supply.  —  In  a  balanced  aquarium,  what  do  the 
fish  eat?     A  fish  or  any  other  living  thing  needs  food  not 
only  to  furnish  fuel  which  may  be  oxidized  to  set  energy 
free,  but  it  must  also  have  food  to  replace  the  waste  which 
is  occurring  in  the  different  parts  of  the  body,  and  for  growth 
if  there  is  any  growth  going  on. 

Foods,  therefore,  may  be  divided  into  energy-producing 
food*  and  tissue-forming  foods.  The  tissue-forming  por- 
tion of  foods  is  made  up  of  complex  substances  called  pro- 


Courttsy  of  New  Yorl  Zoological  SoctetU. 

FIGURE  75.  —  A  BALANCED  AQUARIUM. 


90 


GENERAL   SCIENCE 


teins  and  certain  mineral  salts.  The  proteins,  when  oxidized, 
will  produce  energy,  but  the  chief  energy-producing  portions 
of  food  are  carbohydrates  (starch  and  sugar)  and  fats. 


FIGURE  76.  —  RELATION  OF  PLANT  AND  ANIMAL  IN  A  BALANCED  AQUARIUM. 

Since  fish  of  the  balanced  aquarium  maintain  their  size 
and  are  active,  what  must  be  obtained  from  the  plants? 

Since  the  plants  do  not  decrease  in  quantity,  what  must 
they  be  able  to  do? 


IMPORTANCE  TO  US  OF  THE  OTHER  GASES  OF  THE  AIR     91 

We  already  have  learned  from  what  they  make  carbo- 
hydrates. Explain.  Carbohydrates  in  turn  are  some- 
times changed  by  the  activity  of  the  living  matter  into  fat. 
For  the  manufacture  of  proteins,  the  plant  must  not  only 
have  carbon,  hydrogen,  and  oxygen,  which  may  be  obtained 
from  the  carbon  dioxide  and  water,  but  must  also  have 
nitrogen  and  other  elements.  The  wastes  of  the  fish  con- 
tain all  these  needed  elements. 

In  swimming  about,  the  fish  are  contfnually  exerting 
energy.  What  is  the  final  source  of  this  energy? 

The  relation  of  the  plants  and  animals  in  the  balanced 
aquarium  is  represented  in  the  diagram  (Figure  76)  on  the 
preceding  page. 

What  do  you  think  would  happen  to  animals,  including 
man,  if  there  should  be  no  more  green  plants  ?  Explain. 

Summarize  in  a  sentence  or  two  the  importance  to  us  of 
the  carbon  dioxide  of  the  air. 

INDIVIDUAL  PROJECTS 

1.  Rapidity  of  starch  manufacture  in  a  leaf. 

2.  Keeping  a  balanced  aquarium. 

REPORT 
The  world's  food  supply. 

REFERENCES  FOR  PROJECT  VIII 

1.  The  Fresh  Water  Aquarium  and  Its  Inhabitants,  Eggeling  and 
Ehrenberg.     Henry  Holt  &  Co. 

2.  Life  in  Ponds  and  Streams,  W.  Furneaux.     Longmans,  Green 
&Co. 

3.  The  American  Boys'  Handy  Book,  Beard.     (Fresh  water  and 
Marine  Aquaria.) 


PROJECT  IX 
•      TO   KEEP   FOODS   FROM    SPOILING 

You  know  that  many  foods  if  left  in  the  air  spoil  or  decay. 
Name  some  fogds  which  you  know  will  spoil  if  left  exposed 
to  the  air.  Since  foods  must  be  transported  long  distances 
and  frequently  must  be  kept  many  months  before  being  used, 
the  problem  of  preserving  foods  is  of  the  very  greatest 
importance.  Without  the  means  of  preserving  food  from 
decay  our  present  civilization  could  not  have  arisen, 
i  Think  for  a  moment  of  the  possibility  of  the  existence  of 
great  cities,  like  New  York,  Chicago,  or  of  great  manu- 
facturing centers,  if  ways  of  keeping  foods  from  spoiling  had 
not  been  discovered.  Could  the  United  States  have  sent 
her  great  army  of  2,000,000  men  to  Europe,  if  there  had 
been  no  means  of  preserving  foods  for  many  months  and 
even  years?  In  considering  how  foods  may  be  kept  from 
spoiling,  naturally  the  first  problem  is : 

Problem  1.     What  causes  foods  to  spoil   or   decay?  — 
Is  it  the  oxygen  of  the  air  acting  upon  the  food  which  causes 
the  change,  a  process  of  slow  oxidation  such  as  we  have 
observed   in   a   number   of   cases?     The   question   can   be 
answered  by  performing  -the  following  experiment. 

Experiment.  —  To  find  out  what  causes  foods  to  spoil  when  left 
exposed  to  the  air,  pour  some  beef  tea  made  of  beef  extract  and  a 
small  amount  of  peptone  (digested  protein)  into  two  test  tubes.  Boil 
the  beef  tea  in  each  test  tube  for  an  equal  length  of  time.  Stopper  one 
with  cotton.  Allow  the  other  to  remain  open.  Place  the  tubes  side 
by  side  in  the  room.  (Experiments  have  proved  that  air  will  pass 

92 


.      TO  KEEP  FOODS  FROM  SPOILING  93 

through  a  cotton  stopper  but  that  particles  floating  in  the  air  are 
caught  by  the  cotton.) 

After  a  few  days  observe  the  contents  of  the  tubes.  What 
differences  in  appearance  are  noticeable?  Smell  the  con- 
tents of  each  tube.  What  is  your  conclusion?  Is  oxygen 
alone  able  to  cause  substances  to  decay?  If  a  drop  of  the 
beef  tea  from  the  unstoppered  tube  is  examined  with  a 
high  power  microscope,  a  very  large  number  of  exceedingly 
small  objects  will  be  seen.  Some  are  spherical  and  some 
are  rod-shaped. 

If  even  the  smallest  possible  amount  of  the  spoiled  beef  tea 
is  added  to  the  unspoiled,  stoppered  tea,  the  latter  also  be- 
comes spoiled  in  a  few  days.  Another  examination  of  the 
tea  with  the  microscope  will  show  that  there  has  been  an 
enormous  increase  in  the  number  of  the  spherical  and  rod- 
shaped  bodies.  The  fact  that  they  have  increased  in  number 
is  an  indication  that  they  are  living  bodies.  These  small, 
living  bodies  are.  called  bacteria. 

It  seems  evident  that  the  spoiling  of  the  beef  tea  was 
associated  with  the  development  of  bacteria  within  it. 
Many  experiments  have  shown  that  the  decay  of  plant  and 
animal  (organic)  matter  is  always  brought  about  by  bacteria 
or  their  close  relatives,  the  molds. 

Problem  2.  Where  bacteria  are  found.  —  By  the  follow- 
ing experiments  information  may  be  obtained  concerning 
the  distribution  of  bacteria. 

As  in  these  experiments  it  is  important  to  keep  separate  the 
descendants  of  different  bacteria,  a  solid  or  semi-solid  food 
material  must  be  used.  The  food  mixtures  which  we 
prepare  to  obtain  a  growth  of  bacteria,  are  called  culture 
media.  In  the  previous  experiment  the  beef  tea  was  a 


GENERAL  SCIENCE 


liquid  culture  medium.  A  solid  culture  medium  is  made  by 
adding  to  beef  tea  some  agar-agar,  a  vegetable  gelatine  ob- 
tained from  certain  kinds  of  sea  weeds.  (Details  of  prepa- 
ration are  given  in  the  appendix.)  Into  Petri  dishes  (flat 
dishes  especially  designed  for  study  of  bacteria)  which  have 
been  highly  heated  to  kill  any  living  organisms  present,  pour 
some  of  this  melted  agar  medium.  Cover  the  dishes  imme- 
diately. In  a  short  time  the  culture  medium  will  become 
jellylike  and  ready  for  use. 

Experiment.  —  Expose  open  dishes  in  several  of  the  following 
places  for  five  minutes,  then  close  and  label :  —  a  classroom,  a  corridor 
before  the  passing  of  classes,  a  corridor  during  passing  of  classes,  a  win- 
dow sill  outside  of  room,  street,  subway,  park,  etc. 

Experiment.  —  By  means  of  a  needle,  which  has  been  heated  (ster- 
ilized) to  kill  organisms  upon  it,  put  into  dishes  small  amounts  of 
material  which  you  wish  to  test  for  the  presence  of  microorganisms; 
e.g.  dust  from  floor,  saliva,  dirt  from  under  finger  nails,  milk,  soil,  etc. 

Experiment.  —  Test  various  other  substances,  e.g.  pupil's  finger, 
breath,  paper  and  silver  money,  drinking  water,  the  edge  of  drinking 

cup,  blade  of  a  knife,  pencil 
point,  etc.  Take  care  in 
every  case  that  you  prevent 
the  entrance  of  any  other 
material. 


Describe  the  results  of 
these  experiments.  The 
spots  which  you  see  are 
colonies  of  bacteria  or 
mold  (Figure  77).  Are 
there  indications  of  the 
presence  of  more  than  one  kind  of  microorganisms?  Do 
you  see  any  mold  colonies?  They  are  fluffy  or  hairy  in 
appearance  instead  of  waxy  like  the  bacteria  colonies.  Does 


FIGURE  77. —  COLONIES  OF  BACTERIA  AND 
MOLD. 

The  agar  culture  med  um  in  these  d'shes 
was  exposed  to  the  air  for  about  5  minutes. 


TO  KEEP  FOODS  FROM  SPOILING 


95 


there  seem  to  be  any  connection  between  the  presence  of 
dust  and  the  abundance  of  microorganisms? 

Problem  3.  Size,  shape,  and  method  of  multiplication  of 
bacteria.  —  Could  you  see  the  bacteria  upon  the  agar  plate 
when  the  plate  was  first  exposed  to  the  air?  What  does 
this  indicate  as  to  the  size  of  the  bacteria?  You  will  find 
that  they  can  be  seen  only  with  rather  a  high  power  of  a 
compound  microscope.  \j 

They  are  the  smallest  and  simplest  plant  life  known. 
The  average  rod-shaped  bacterium  measures  about  r^io~o  of 


From,  Household  Bacteriology  by  Buchanan. 
FIGURE  78. — THE  FOUR  TYPES  OF  BACTERIA. 
A,  cocci;  B,  bacilli;  C,  spirilla;  D,  branched  filamentous  organism. 

an  inch  in  length  and  about  50000  of  an  inch  in  diameter. 
Some  are  larger  and  many  are  much  smaller,  some  being 
so  small  that  they  are  invisible  under  the  highest  power 
lenses,  but  known  to  be  present  because  of  the  effect  which 
they  produce  in  the  substance  in  which  they  are  living.  A 
calculation  of  the  number  in  a  cubic  inch  of  average  sized 
bacteria  will  give  you  some  idea  of  the  extreme  smallness 
of  these  plants. 

If  you  are  fortunate  enough  to  have  a  compound  micro- 
scope for  the  use  of  your  class  you  may  observe  the 
shape  of  the  bacteria.  If  no  microscope  is  available,  examine 


96  GENERAL   SCIENCE 

the  drawings  representing  the  different  shapes.  It  will  be 
noted  that  there  are  three  principal  forms  of  bacteria; 
spherical  or  ball-shaped  (coccus),  rod-shaped  (bacillus), 
and  spiral-shaped  (spirillum)  (Figure  78). 

They  multiply  by  dividing  into  two.  These  in  turn,  after 
growing  to  full  size,  will  again  divide.  If  conditions  are 
favorable,  bacteria  may  grow  to  full  size  and  divide  again  in 
thirty  minutes.  It  has  been  estimated  that  if  bacterial 
multiplication  went  on  unchecked  and  the  division  of  each 
bacterium  took  place  as  often  as  once  an  hour,  the  descend- 
ants of  each  individual  would  in  two  days  number  281,500,- 
000,000.  Actually,  such  unchecked  multiplication  never 
occurs  except  for  a  very  short  period,  as  conditions  develop 
which  interfere  with  further  growth. 

Not  all  microorganisms  are  bacteria.  Yeasts  and  molds 
are  rather  closely  related  to  the  bacteria.  There  are  also 
animals  (protozoa)  of  approximately  as  simple  structure  as 
the  bacteria.  Some  of  these,  because  of  the  harm  that  they 
do,  are  of  very  great  interest  to  us. 

Since  these  extremely  small  living  things  cause  our  food  to 
decay,  it  is  important  that  we  know  the  conditions  which 
are  favorable  and  conditions  which  are  unfavorable  for  their 
growth,  hence  our  next  problem  is : 

Problem  4.  What  conditions  are  favorable  and  what  un- 
favorable for  growth  of  bacteria  and  molds  ?  —  This  problem 
can  best  be  solved  by  a  number  of  experiments. 

Experiment.  —  Take  a  number  of  test  tubes,  and  into  each  pour 
about  an  inch  of  the  beef  tea  culture  medium  to  which  has  been  added 
some  material  known  to  contain  bacteria. 

1.  Stopper  two  tubes  with  cotton.  Put  one  in  a  warm  place,  near 
a  radiator  or  stove  and  the  other  in  a  cold  place,  as  in  the  ice  box. 


TO  KEEP  FOODS  FROM  SPOILING  97 

2.  Take  two  test  tubes.     Boil  the  contents  of  one.     Stopper  both 
tubes  with  cotton  and  keep  both  under  the  same  conditions. 

3.  Into  one  of  three  test  tubes  put  all  the  salt  that  will  dissolve  in 
the  beef  tea.     Into  the  second  put  one  half  the  quantity  of  salt  placed 
in  the  first.    Put  nothing  in  the  third. 

4.  Into  one  of  three  test  tubes  put  an  amount  of  sugar  equal  to  the 
amount  of  beef  tea.     Into  the  second  put  one  half  this  amount  of  sugar. 
Put  nothing  in  the  third. 

After  a  few  days,  examine  the  various  test  tubes  for  bacteria.  What 
is  the  apparent  effect  on  bacteria  of  (1)  warmth,  (2)  boiling,  (3)  salt, 
(4)  sugar? 

Experiment,  —  Expose  to  the  air  for  ten  minutes  several  Petri 
dishes  containing  agar  culture  medium.  Paste  over  the  covers  black 
paper  from  which  have  been  cut  large  letters  for  purposes  of  iden- 
tification. Put  the  dishes  where  they  will  be  exposed  to  sunlight. 
Examine  after  several  weeks.  Record  the  result. 

Experiment.  —  Expose  to  the  air  a  Petri  dish  which  has  been  kept 
until  the  culture  medium  has  become  dry. 

The  facts  which  we  have  learned  from  these  experiments       f 
have  many  applications  both  in  our  home  life  and  commer- 
cially.    Some  of  these  which  most  concern  us  in  our  every- 
day life  should  be  considered. 

Problem  5.  Use  of  cold  in  the  home  in  checking  the 
growth  of  bacteria.  .  (a)  You  at  once  think  of  the  ice  chest 
or  refrigerator.  Let  us  see  if  we  can  understand  how  the 
refrigerator  is  so  effective  in  preserving  our  milk,  meats,  and 
vegetables.  First,  why  is  ice  used  in  a  refrigerator?  You 
will  at  once  say,  because  it  is  cold;  but  you  know  that  a 
block  of  wood  or  stone  or  iron  which  might  be  just  as  cold 
is  never  used  in  place  of  ice.  The  reason  for  this  use  of  ice 
may  be  illustrated  by  the  following  experiment. 

Experiment.  —  Nearly  fill  two  beaker  glasses  with  water  of  the  same 
temperature.  Note  the  temperature.  Place  in  one  of  the  glasses 
a  piece  of  ice  and  in  the  other  a  stone  of  equal  size  which  has  been  kept 


GENERAL  SCIENCE 


on  ice  and  has  the  same  temperature.  Place  the  two  glasses  side  by 
side  and  apply  gradually  an  equal  amount  of  heat.  Note  the  tem- 
perature from  time  to  time.  Result?  What  effect  does  the  melting 

of  ice  have  upon  the  heat 
of  the  surrounding  water? 
Is  this  not  what  you  would 
expect?  The  removal  of 
heat  from  water  causes  it 
to  change  into  ice,  so  heat 
must  be  used  up  to  change 
the  ice  back  into  water. 
Do  you  think  that!  your  re 
frigerator  will  be  made  colder 
by  covering  the  ice  with 
pads  to  keep  it  from  melt- 
ing? 


s        07  id   y 
Courtesy  of  McCray  Refrigerator  Co. 

FIGURE  79.  —  WALL  OF  A  REFRIGERATOR. 


An  ice  chest  or  refrigerator  is  essentially  a  box  whose  walls 
are  so  constructed  that  they  are  poor  conductors  of  heat 
(Figure  79).  This  is  usually  accomplished  by  having  in  the 
wall  an  air  space  which  is  packed 
with  charcoal  or  some  other  poor 
conductor.  The  ice  in  a  refrigera- 
tor should  be  placed  near  the 
top.  The  melting  of  the  ice  cools 
the  air  in  contact  with  it.  The 
cold  air  falls.  (Why?)  In  so 
doing  it  forces  the  warm  air  to 
the  top  where  it  in  turn  is  cooled 
and  replaces  the  air  which  has 
been  warmed  by  coming  in  con- 
tact with  the  food.  The  effective- 
ness of  the  refrigerator  depends 
upon  the  circulation  of  air  within 
it;  and  accordingly  care  should 


FIGURE  80.  —  CURRENTS  OF  AIR 
IN  A  REFRIGERATOR. 


TO  KEEP  FOODS  FROM  SPOILING  99 

be  taken  that  the  free  passage  of  air  is  not  obstructed  in 
any  way  (Figure  80). 

The  ice  chest  is  simply  a  means  of  checking  the  develop- 
ment of  bacteria  but  by  no  means  does  it  stop  their  growth. 
In  a  large  ice  chest,  food  may  be  preserved  for  a  considerable 
length  of  time  but  it 
finally  will  decay.  In 
small  ones,  food  may  be 
kept  for  only  a  few  days. 
All  refrigerators  should 
be  frequently  cleaned,  as 
dirt  and  particles  of  fo6"d 
furnish  a  place  for  the 
growth  of  bacteria,  and 
after  a  time  render  the 
refrigerator  unfit  for  use. 

Various  methods  have 
been  used  in  homes  where 
ice  cannot  be  obtained  to 
provide  a  low  tempera- 
ture for  the  protection 
of  food  against  the  ac- 
tion of  bacteria.  Cool 
cellars,  cold  running 
water,  spring  houses,  and  FlGURE  81— 1CELESS 
suspension  in  deep  wells  are  means  frequently  employed. 
An  iceless  refrigerator  (Figure  81)  may  be  made  as  follows : 

Cover  a  frame  of  wood  with  cloth  such  as  duck  (Figure 
82).  Sew  a  number  of  lamp  wicks  to  the  edge  of  the  cloth 
and  allow  the  other  end  of  the  wicks  to  extend  into  a  vessel 
of  water  on  top  of  the  frame.  The  water  soaks  into  the 
cloth  through  the  wicks.  As  heat  is  used  up  in  evaporation 


100 


GENERAL  SCIENCE 


of  water,  the  temperature  within  the  refrigerator  is  lowered 
to  50-56  degrees  F.     The  efficiency  of  this  refrigerator  is, 
increased  if  it  is  kept  where  there  is  a  current  of  air.     Why  ? 

In  tropical  countries, 
drinking  water  is  kept 
in  porous  earthenware 
jars.  Why? 

Problem  6.  Use  of 
cold  in  storage  ware- 
houses.—  In  cold-storage 
plants  low,  constant  tem- 
peratures are  maintained. 
Definite  temperatures  are 
kept  in  different  rooms, 
as  not  all  foods  are  best 
preserved  at  the  same 
temperature.  Fruits  are 
stored  at  a  little  above 
freezing;  fresh  meat,  at 
about  25  degrees  F. ; 
poultry,  at  about  15  de- 
grees F. ;  fish,  at  about 
0  degrees  F. 

The  question  arises, 
How  are  these  steady  low 
temperatures  produced,?  As  ice  is  not  used,  a  review  of  the 
principle  of  the  iceless  refrigerator  may  help  us.  (Explain 
the  production  of  low  temperature  in  the  iceless  refrigerator.) 
Cold-storage  plants  generally  use  ammonia  which  has 
been  changed  into  a  liquid  from  a  gas  by  pressure.  When 
the  pressure  is  released  the  ammonia  returns  to  its  gaseous 


FIGURE  82.  —  FRAMEWORK  OF  AN  ICELESS 
REFRIGERATOR. 


TO  KEEP  FOODS  FROM 


105 


state,  taking  heat  from  everything  arcuftd  -it  : 

The  effect  of  rapid  evaporation  (changing  a  liquid  into  a 

gas)  may  be  illustrated  by  the  following  experiment. 

Experiment.  —  Place  some  chloroform  or  ether  in  a  thin  watch 
crystal.  Place  the  crystal  upon  a  drop  of  water.  Through  a  tube  blow 
a  current  of  air  upon  the  chloroform  or  ether.  As  soon  as  it  all  has 
evaporated,  notice  the  condition  of  the  water.  Result?  Conclusion? 


Cold  Water 


Co  Sewer 


-Regulating  Valve- 


FIGURE  83.  —  ICE  PLANT. 

Ammonia  which  has  been  made  liquid  passes  slowly  through  the  regulating 
valve  into  pipes  in  which  the  pressure  is  very  low.  The  ammonia  quickly 
changes  into  a  gas,  absorbing  heat  in  doing  so  from  everything  around  it. 
The  ammonia  gas  is  removed  by  the  pump  at  the  left  of  the  figure  and  is 
changed  again  by  pressure  and  the  spray  of  cold  water  into  liquid  ammonia. 

The  development  of  cold  storage  has  been  of  great  advan- 
tage both  to  producers  and  to  consumers.  Consider  the 
condition  which  existed  before  the  use  of  cold  storage  in 
the  peach  region  of  Michigan  for  example.  Thousands  of 
bushels  of  peaches  ripened  in  a  few  weeks,  with  the  result 
that  the  Chicago  markets  were  swamped.  Prices  went 
down  to  almost  nothing ;  but  even  then  enormous  quantities 
rotted.  Sometimes  the  money  received  for  the  peaches 
was  not  sufficient  to  pay  the  transportation  and  brokerage 


102 


GENERAL  SCIENCE 


,  ,aq.d  ;the  fruit  growers  received  nothing  for  their 
year's  work.  Did  the  people  of  Chicago  profit  by  this 
condition?  It  is  true  that  for  a  short  time  peaches  could 
be  bought  for  a  very  low  price;  the  peach  season  was, 
however,  made  extremely  short. 

Since  great  storage  plants  have  been  built,   conditions 
have   changed   entirely.     Now,   only   enough   fruit   is  put 


FIGURE  84.  —  STORAGE  OF  BUTTER  IN  A  REFRIGERATING  PLANT. 

upon  the  market  to  supply  the  normal  demands;  the 
surplus  is  put  into  cold  storage  warehouses  to  be  taken 
out  and  sold  as  the  supply  direct  from  the  orchards  de- 
creases. The  producer  now  receives  a  fair  return  for  his 
labor  and  investment.  The  consumer  has  a  lengthened 
peach  season  and  there  is  a  minimum  of  waste. 

It  is  now  possible  to  have  fresh  at  any  season  of  the  year 
the  perishable  foods  produced  at  almost  any  other  season. 


TO  KEEP  FOODS  FROM  SPOILING  103 

Without  cold  storage  the  supply  of  such  foods  as  butter  and 
eggs  and  some  other  foods  would  be  so  limited  at  certain 
times  of  the  year  that  they  could  be  used  only  by  the  wealth- 
iest people  (Figure  84). 

By  means  of  cold-storage  cars  and  ships,  perishable  foods 
may  be  transported  almost  any  distance.  American  fresh 
meat  is  sold  in  the  markets  of  London  and  Paris.  Argentine 
beef  is  put  on  sale  in  American  cities.  Fruits  of  California 
and  the  southern  states  are  delivered  with  little  or  no  loss 
of  flavor  to  every  city  in  the  country. 

Problem  7.  Use  made  of  heat  in  food  preservation.  — 
A  visit  to  a  grocery  store  and  observation  of  the  rows  of 
canned  vegetables,  fruits,  and  meats  are  sufficient  to  indicate 
the  great  use  made  of  this  method  of  preserving  food.  It  is 
one  of  the  chief  agencies  by  which  a  regular  and  varied  food 
supply  is  made  possible.  Without  the  modern  methods  of 
food  preservation,  cities  such  as  New  York,  Philadelphia, 
and  Chicago  could  not  exist. 

Experiment.  — •  Open  a  can  of  meat  of  some  kind,  permit  some  of  the 
contents  to  be  exposed  to  the  air  for  a  day.  Put  portions  of  the  meat 
into  two  test  tubes.  Place  one  test  tube  in  boiling  water  for  an  hour. 
Stopper  both  test  tubes  with  corks,  dipping  the  stoppered  ends  into 
melted  paraffin  to  make  them  air-tight.  Put  the  test  tubes  aside  in 
a  warm  place  for  a  few  days.  Result  ?  Conclusion  ? 

Pasteurization  of  Milk.  —  As  diseases  may  be  transmitted 
by  milk,  the  problem  of  destroying  bacteria  contained  by 
it  is  of  great  importance.  Tuberculosis,  typhoid  fever, 
scarlet  fever,  diphtheria,  and  very  probably  dysentery, 
are  diseases  spread  by  milk.  The  problem  is  rendered  more 
difficult  by  the  fact  that  boiling  affects  milk  injuriously  to 
some  exterit,  causing  it  to  become  less  digestible.  It  has 
been  found  that  by  heating  milk  to  a  temperature  of  142 


104  GENERAL  SCIENCE 

to  145  degrees  F.  for  at  least  thirty  minutes,  the  pathogenic 
(disease-producing)  germs  will  be  killed  without  injuring  the 
digestible  qualities  of  the  milk.  This  process  is  known  as 
pasteurization.  Hospital  records  show,  however,  that  it  is 
advisable  to  give  orange  juice  to  children  whose  diet  is 
almost  exclusively  pasteurized  milk.  Otherwise,  rickets  (a 
disease  of  the  bones)  or  another  disease  known  as  scurvy 
may  develop. 

Problem  8.  Use  made  of  other  methods  of  food  pres- 
ervation. —  What  methods  for  preserving  food  in  addition 
to  use  of  cold  and  extreme  heat  can  you  think  of? 

The  use  of  sugar  to  preserve  food  may  be  shown  by  the 
following  experiment. 

Experiment.  —  Put  some  pieces  of  fruit  into  a  test  tube  and  cover 
loosely  to  prevent  drying.  Cover  some  similar  pieces  of  fruit  with 
melted  sugar.  Slightly  heat  the  mixture  of  sugar  and  fruit,  put  into 
test  tube  and  cover  in  the  same  way  as  the  other  tube  was  covered. 
Put  both  tubes  aside  in  a  warm  place.  Result  ?  Conclusion  ? 

Jellies  and  marmalades  are  examples  of  the  use  of  sugar 
as  a  food  preservative.  From  one  of  our  experiments,  what 
was  your  opinion  as  to  the  amount  of  sugar  that  should  be 
used?  If  a  smaller  percentage  is  used,  yeast  will  cause 
fermentation  with  resulting  bubbles  of  gas  and  an  odor  of 
alcohol.  Before  canning  became  common,  this  method  of 
preservation  was  much  more  used  than  at  present.  The 
large  percentage  of  sugar  causes  some  modification  in  the 
flavor  of  the  food,  and  makes  the  material  more  of  a  sweet- 
meat than  a  fruit  food.  Condensed  milk,  which  has  come 
into  such  general  use,  remains  unspoiled  for  a  considerable 
time  after  the  can  has  been  opened  because  there  has  been 
added  to  it  30  to  40  per  cent  of  sugar. 


TO  KEEP  FOODS  FROM  SPOILING  .      105 

The  use  of  salt  as  a  food  preservative  is  also  very 
common. 

Experiment.  —  Put  small  pieces  of  fresh  fish  into  two  test  tubes. 
Cover  the  fish  in  one  tube  with  brine  (a  saturated  mixture  of  salt  and 
water).  Put  aside  in  a  warm  place.  Result?  Conclusion? 

Although  salt  preserves  food  from  decay,  the  flavor 
of  the  material  is  considerably  changed  and  it  is  usually 
less  easily  digested  than  when  fresh.  In  many  cases  it 
is  wise  to  soak  the  salty  food  in  water  before  it  is 
prepared  for  the  table.  Meats  and  fish  are  frequently  pre- 
served in  brine.  Eggs  are  also  sometimes  preserved  in  the 
same  way.  Salted  butter  can  be  kept  fresh  and  of  good 
flavor  much  longer  than  unsalted  butter.  Salt  is  used  in 
connection  with  other  methods  of  preservation  such  as 
drying  and  smoking. 

Use  of  vinegar  and  spices.  —  Name  foods  that  you  know 
are  preserved  in  vinegar.  Sauerkraut  is  cabbage  which 
has  produced  in  itself,  by  the  process  of  fermentation,  an  acid 
similar  to  that  of  vinegar,  which  protects  it  from  further 
decomposition.  Most  of  the  spices  used  in  the  home  have 
some  antiseptic  properties.  Mince-meat  is  a  good  example 
of  the  ability  of  spices  to  prevent  decay.  In  the  same  way, 
the  spices  in  sausages  not  only  give  a  desirable  flavor  but 
also  prevent  rapid  spoiling.  Spices,  however,  are  only 
mildly  antiseptic  and  are  consequently  of  little  value  in 
this  respect  except  when  used  in  cold  weather. 

Drying  and  smoking  are  other  methods  of.  preserving  foods. 

Experiment.  —  Put  some  raisins  which  have  been  soaked  in  water 
for  a  day  into  a  test  tube.  Into  another  test  tube  put  some  unsoaked 
•  raisins.  Put  aside  in  a  warm  place.  Result?  Conclusion? 

Next  to  canning,  drying  is  the  most  important  method 
of  preserving  food.  Compare  flour  which  has  been  kept 


106  GENERAL   SCIENCE 

dry  with  some  which  has  been  kept  slightly  moist  for  a 
week.  In  the  same  way  compare  bean  and  pea  seeds  and 
grains  of  corn  and  wheat  which  have  been  kept  dry  with  the 
same  kinds  of  seeds  that  have  been  soaked  and  permitted  to 
remain  moist.  What  is  an  advantage  of  hard-tack  and 
crackers  over  bread?  When  fruits  are  completely  dried, 
their  flavor  is  largely  lost.  Those  which  contain  a  large 
percentage  of  sugar,  such  as  grapes,  prunes,  peaches,  figs, 
dates,  currants,  etc.,  may  be  preserved  by  the  removal  of 
only  a  limited  portion  of  their  water  by  drying.  Why? 

Meats  are  preserved  on  an  immense  scale  by  a  combination 
of  salting,  drying,  and  smoking.  Give  examples.  Milk  is 
dried  and  put  upon  the  market  as  a  powder.  When  dis- 
solved in  water  it  has  a  flavor  slightly  different  from  that 
of  fresh  milk,  but  none  of  its  nutritive  properties  has  been 
lost.  It  possesses  the  advantages  of  occupying  little  space 
in  transportation,  and  of  being  able  to  be  kept  indefinitely 
without  decaying,  souring,  or  molding.  Evaporated  milk  has 
had  a  portion  of  its  water  removed,  thus  greatly  reducing  its 
bulk. 

Briefly  sum  up  the  main  points  you  have  learned  as  to 
how  to  keep  foods  from  spoiling,  and  why  these  methods  are 
successful. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Examination  of  bacteria  with  a  microscope.    Make  drawings. 

2.  -Making  of  agar  culture  medium. 

3.  Can  a  dozen  jars  of  vegetables  or  fruit. 

4.  Construct  a  homemade  device  for  pasteurizing  milkT 

5.  Make  six  glasses  of  jelly. 

6.  Construct  an  apparatus  for  dehydration  of  vegetables.    Dehy- 
drate some  vegetables  that  are  difficult  to  keep  through  the  winter. 
Cook  and  test. 

7.  Construction  of  an  iceless  refrigerator. 


TO  KEEP  FOODS  FROM  SPOILING  107 

REFERENCES  FOR  PROJECT  IX 

1.  Bacteria,  Yeasts  and  Molds  in  the  Home,  W.  H.  Conn.     Ginn 
&Co. 

2.  Household  Bacteriology,  E.  D.  Buchanan. 

3.  Milk  and  Its  Products,  H.  H.  Wing.     Macmillan  Company. 

4.  An  Iceless  Refrigerator.     Food  Thrift  Series  No.  4,  U.  S.  Depart- 
ment of  Agriculture. 

5.  Farmers'  Bulletins,  U.  S.  Department  of  Agriculture: 
375.    Care  of  Food  in  the  Home. 

521.    Canning  Tomatoes  at  Home  and  in  Club  Work. 

839.    Canning  by  the  Cold-Pack  Method. 

841.   Drying  Fruits  and  Vegetables  in  the  Home. 

6.  Circulars,  U.  S.  Departm't  of  Agriculture,  Canning,  Evaporating. 
7'  Cold  Pack  Canning.    International  Harvester  Company,  Chicago. 


PROJECT  X 

TO   PROTECT   OURSELVES   AGAINST   HARMFUL 
MICROORGANISMS 

MICROORGANISMS  can  do  many  things  beside  causing  foods 
to  decay.  Some  do  very  valuable  work;  so  valuable  in 
fact,  that  without  their  aid  life  would  cease  to  exist  upon  the 
earth.  Qn  the  other  hand,  some,  such  as  the  disease- 
producing  (pathogenic)  forms,  are  extremely  harmful, 
causing  the  premature  death  of  many  persons. 

Fortunately  the  large  majority  of  microorganisms  are 
not  pathogenic.  If  this  were  not  true,  we  might  well  be 
appalled  at  the  results  of  our  experiments  as  to  the  dis- 
tribution of  bacteria.  Most  of  the  bacteria  discovered  in 
those  experiments  are  capable  of  producing  decay  only,  but 
it  must  not  be  forgotten  that  the  objects  and  substances 
examined,  while  they  are  often  carriers  of  non-pathogenic 
bacteria  alone,  still  may  frequently  be  carriers  of  disease- 
producing  ones.  . 

In  considering  how  to  protect  ourselves  from  harmful 
microorg  nisms,  we  must  consider  how  they  affect  us,  how 
the  microorganisms  (germs)  may  be  carried  from  one 
person  to  another,  how  the  body  naturally  fights  the  germs, 
how  the  body  may  be  given  special  power  to  fight  them,  and 
finally  how  certain  substances  called  disinfectants  and 
antiseptics  may  be  used  to  destroy  germs. 

Problem  I.  How  bacteria  and  other  microorganisms 
affect  the  health.  —  What  frequently  happens  when  you  get  a 

108 


TO  PROTECT  OURSELVES  AGAINST  MICROORGANISMS       109 

splinter  in  your  finger?  It  has  been  found  that  if  the  splin- 
ter was  free  from  bacteria  no  irritation  resulted.  What 
is  your  conclusion  ?  The  red,  swollen,  and  painful  condition 
(inflammation)  is  now  known  to  be  due  to  poisons  or  toxins 
which  are  produced  by  certain  bacteria  which  were  on  the 
splinter. 

Usually  after  a  short  time  the  inflammation  vanishes, 
and  a  small  amount  of  pus  appears  which  should  be  removed 


FIGURE  85.  —  DEAD  CHESTNUT  TREES. 

These  trees  along  a  road  in  New  York  State  were  killed  by  the  chestnut 
bark  disease. 

with  a  needle  which  has  been  passed  through  a  flame  and 
the  broken  place  in  the  skin  washed  with  an  antiseptic, 
a  substance  that  kills  or  checks  the  growth  of  bacteria. 
The  pus  is  produced  by  the  action  of  white  blood  corpuscles 
which  have  attacked  and  destroyed  the  bacteria.  Some- 
times, however,  the  bacteria  are  not  destroyed  and  the  in- 


110  GENERAL   SCIENCE 

flammation  may  spread  and  possibly  finally  develop  into 
blood  poisoning. 

The  inflammation  of  pimples  and  boils  is  also  caused  by 
bacteria,  and  the  pus  is  formed  in  the  same  way. 

You  have  all  noticed  that  if  one  member  of  a  family 
gets,  a  cold  frequently  the  other  members  also  contract  it. 
Microscopic  examinations  have  shown  that  bacteria  of 
certain  kinds  are  always  associated  with  colds.  It  is  very 
evident  that  this  inflammation,  as  in  other  cases  of  in- 
flammation, is  due  to  the  production  of  poisons  or  toxins 
by  the  bacteria. 

In  the  case  of  colds  a  congestion  of  blood  in  some  organ 
as  in  the  lining  of  the  nose,  throat,  or  intestine  offers  a 
favorable  condition  for  the  development  of  bacteria.  Pre- 
vention of  unusual  chilling  of  any  part  of  the  body  will 
assist  in  the  avoidance  of  colds,  as  congestion  of  blood  will 
then  be  prevented.  It  is  especially  important  to  avoid 
chilling  the  body  when  one  is  fatigued  or  tired,  as  then  there 
is  greater  susceptibility  to  disease.  Regular  and  sufficient 
muscular  exercise,  avoidance  of  overeating,  and  good 
habits  of  sleep  and  rest  are  other  conditions  that  enable 
the  body  to  resist  the  bacteria  which  cause  colds. 

Microscopic  examination  has  shown  that  the  decay  of 
teeth  and  diseased  conditions  of  the  tonsils  are  due  to  the 
growth  of  bacteria.  The  seriousness  of  the  growth  of 
bacteria  in  decayed  teeth  and  in  the  tonsils  is  only  beginning 
to  be  realized.  The  bacteria  or  the  poisons  produced  by 
them  may  be  carried  by  the  circulatory  system  to  other 
organs  and  there  cause  serious  diseases.  Certain  forms  of 
rheumatism,  mental  diseases,  digestive  troubles,  etc.,  are 
cured  by  getting  rid  of  these  breeding  places  for  bacteria. 
The  teeth  are  also  liable  to  a  disease  known  as  Riggs'  disease, 


TO  PROTECT  OURSELVES  AGAINST  MICROORGANISMS      111 

or  pyorrhea,  which  consists  in  the  formation  of  an  abscess  or 
pus  cavity  between  the  roots  and  the  jaw  bone,  causing  the 
teeth  to  loosen  and  in  some  cases  to  fall  out.  This  disease 
is  not  caused  by  bacteria,  which  are  microscopic  plants, 
but  by  simple  animals  called  amoeba. 

With  very  few  exceptions  diseases  are  produced  by 
microorganisms,  chiefly  bacteria.  Since  the  micn> 
organisms  (germs)  which  cause  these  diseases  may  be  trans- 
ferred in  various  ways  from  one  person  to  another,  the 
diseases  are  called  communicable.  The  better  known 
diseases  of  this  kind  are :  tuberculosis,  typhoid  fever, 
influenza,  diphtheria,  scarlet  fever,  measles,  chicken-pox, 
summer  complaint  of  children,  dysentery,  smallpox,  lock- 
jaw, mumps,  Asiatic  cholera,  infantile  paralysis,  malaria, 
yellow  fever,  etc.  In  a  few  of  the  diseases  mentioned 
above,  the  germ  which  is  believed  to  cause  the  disease  has 
not  been  seen  with  the  microscope,  but  the  way  in  which 
those  diseases  develop  and  are  transmitted  indicates  that 
they  are  caused  by  living  germs. 

Problem  2.  How  disease  germs  may  pass  from  one 
person  to  another.  —  Naturally  in  considering  this  problem 
for  any  disease,  we  must  consider  how  the  germs  le  ve  the 
body  of  the  person  having  the  disease  and  how  they  may  get 
into  the  body  of  the  well  person.  Germs  usually  leave  the 
body  in  the  fine  particles  of  moisture  given  out  in  sneezing 
or  coughing  or  in  the  sputum  or  other  excretions  of  the 
body,  and  occasionally  by  blood  sucked  up  by  insects. 
Suggest  ways  by  which  disease  germs  may  gain  entrance  to 
the  body. 

The  problem  will  be  considered  from  the  standpoint  of  a 
few  of  the  most  common  diseases. 


112  GENERAL   SCIENCE 

Tuberculosis  or  consumption.  —  The  most  usual  form  of 
this  disease  is  tuberculosis  of  the  lungs.  How  do  you  think 
the  germs  may  reach  the  outside  of  the  body?  A  well 
person  may  contract  the  disease  by  breathing  in  the  germs 
or  in  some  way  getting  them  into  his  mouth.  Make  a  list 
of  the  ways  in  which  the  germs  of  this  disease  might  pass 
from  a  sick  person  to  a  well  person. 

It  has  been  found  that  the  principal  ways  in  which  the 
germs  of  this  disease  are  carried  from  one  person  to  another 
are :  (1)  by  personal  contact  of  sick  with  well  person, 
especially  by  kissing;  (2)  by  objects  handled  or  put  into 
the  mouth,  as  by  food,  forks,  drinking  cups,  pencils,  or 
towels;*  (3)  by  fine  droplets  given  off  in  coughing  or  while 
talking,  (this  is  probably  one  of  the  most  common 
methods) ;  (4)  by  dust  containing  dried  sputum ;  (5)  by 
milk  or  meat  of  tuberculous  animals. 

Typhoid  fever.  —  In  a  person  sick  with  this  disease  the 
germs  are  developing  in  the  walls  of  the  intestine.  How 
do  you  think  the  germs  escape  from  the  body?  How  do 
you  think  that  they  may  ever  reach  the  intestine  of  a  well 
person  to  begin  growing  there  to  produce  the  poisons  of  the 
disease  ? 

Typhoid  fever  germs  are  taken  into  the  body  with  food 
and  drink.  It  hardly  seems  possible  that  anyone  should  ever 
contract  typhoid  fever  when  we  realize  that  the  germs  leave 
the  diseased  person  in  the  excretions  of  the  body.  However, 
food  and  drink  may  become  polluted  in  a  number  of  ways. 
Water  may  become  contaminated  by  sewage;  milk,  by  the 
unclean  hands  of  milkers ;  oysters  or  clams,  by  growing  near 
the  outlet  of  sewers ;  vegetables,  by  manure ;  fruits  and  ber- 
ries, by  filthy  hands ;  foods  of  all  kinds,  by  flies  which  have 
been  crawling  over  the  excretions  of  a  typhoid  patient. 


TO  PROTECT  OURSELVES  AGAINST  MICROORGANISMS       113 

Suggest  means  to  be  taken  to  prevent  the  spread  of 
typhoid  germs. 

Unfortunately,  persons  who  are  immune  to  the  disease 
may  yet  have  the  germs  produced  in  their  bodies,  and  be 
unconscious  sources  of  infection.  Thus  we  sometimes  read 
of  such  carriers  of  germs  as  "  Typhoid  Mary  "  of  New  York 
City  who,  though  perfectly  well  themselves,  are  a  greater  men- 
ace to  the  public  than  persons  who  are  ill  with  the  disease. 

Other  diseases  may  be  transmitted  in  some  of  the  ways 
in  which  tuberculosis  and  typhoid  fever  are  transmitted, 
while  some  are  carried  by  somewhat  different  methods. 
Diphtheria  is  a  disease  of  the  throat.  Suggest  how  it  might 
be  transmitted,  and  how  its  spread  may  be  prevented.  The 
germ  that  is  supposed  to  cause  influenza  is  found  in  the 
secretions  of  the  mouth  and  nose  of  patients.  Suggest 
means  by  which  it  may  be  spread. 

Tetanus  or  lockjaw  is  produced  by  germs  which  are 
common  in  soil.  They  will  not  develop  in  man  unless 
injected  into-  the  body  along  with  considerable  dirt  in  a 
wound  that  closes  up  and  prevents  the  access  of  'air.  Wounds 
caused  by  rusty  nails  and  toy  pistol  explosions  are0  especially 
favorable  for  the  development  of  tetanus.  How  should  a 
wound  of  this  kind  be  treated  to  prevent  the  development  of 
tetanus  ? 

The  germs  of  pneumonia  are  present  in  the  lungs  and  air 
passages.  Suggest  possible  means  of  infection.  Malaria 
germs  are  carried  from  one  person  to  another  by  a  certain 
kind  of  mosquito  which  lives  near  swamps  and  flies  only  at 
night.  How  can  one  protect  himself  from  this  disease? 

Problem  3.  How  the  body  fights  disease.  —  Considering 
the  ease  with  which  disease  germs  may  enter  the  body,  it 


114  GENERAL   SCIENCE 

may  seem  strange  that  a  person  is  not  constantly  ill  with 
some  disease.  We  know,  however,  that  not  every  person 
exposed  to  infection  contracts  the  disease.  There  are  a 
number  of  reasons  for  this. 

What  is  the  effect  of  the  unbroken  skin?  What  happens 
to  large  amounts  of  dirt  and  dust  of  the  air  which  is  breathed 
in  through  the  nose  ?  What  is  the  appearance  of  the  mucus 
which  is  blown  out  of  the  nose  after  you  have  been  working 
in  a  very  dusty  place  ?  Not  only  does  the  mucus  catch  some 
of  the  germs  that  are  breathed  in  and  permit  their  removal 
but  it  has  been  found  that  it  possesses  some  power  to  kill 
the  germs.  Suggest  one  reason  for  breathing  through  the 
nose  rather  than  through  the  mouth. 

Even  though  these  outer  defenses  of  the  body  are  passed, 
the  germs  are  not  permitted  to  develop  unchecked.  The 
body  offers  a  certain  resistance  to  the  attacks,  partially  by 
means  of  the  white  blood  corpuscles  which  engulf  the  bac- 
teria, and  partially  by  the  resistant  power  of  the  blood  and 
living  parts  of  the  body,  a  power  which  is  not  so  easily  under- 
stood. 

This  power  of  resistance  is  affected  by  a  number  of  things. 
The  fact  that  certain  diseases  occur  only  in  childhood 
indicates  that  age  is  one  of  the  factors  concerned.  A  poor 
diet,  excessive  fatigue,  extremes  of  heat  and  cold,  lack  of 
sleep,  lack  of  fresh  air,  and  weakness  from  other  diseases 
are  conditions  which  lessen  the  power  of  the  body  to  resist 
disease.  In  general,  any  condition  which  increases  the 
health  of  the  body  increases  its  power  to  resist  disease. 
Because  of  this  fact, 'outdoor  life,  deep  breathing,  moderate 
exercise  taken  regularly,  a  proper  amount  of  sleep,  and  good 
food  are  not  only  the  preventives  of  disease  but  in  some 
cases  constitute  a  cure  by  giving  the  body  a  chance  to 


TO  PROTECT  OURSELVES  AGAINST  MICROORGANISMS       115 

fight   off  the  enemy   that   has  already   gained  a  foothold 
(Figure  86). 

Problem  4.  How  the  body  acquires  special  power  to 
fight  disease.  —  You  already  have  some  information  that 
proves  to  you  that  special  ability  to  fight  disease  may  be 
acquired  by  the  body.  A  child  has,  had  whooping  cough, 
or  mumps,  or  measles.  Does  this  have  any  effect  upon  his 


FIGURE  86.  —  A  FRESH  AIR  CAMP  IN  CALIFORNIA. 

chance  of  taking  the  disease  again?  What,  therefore,  is 
your  conclusion  as  to  the  effect  of  having  had  a  disease  upon 
the  ability  of  the  body  to  fight  that  disease  ? 

Based  upon  this  fact,  it  has  been  discovered  that  the  body 
may  be  made  immune  to  certain  diseases  or  protected  against 
them.  You  know  of  a  number  of  such  cases.  Why  is 
smallpox  not  the  common  disease  it  was  several  hundred 
years  ago  ?  How  are  the  soldiers  protected  against  typhoid 


116  GENERAL   SCIENCE 

fever?  Why  is  diphtheria  not  the  dreaded  disease  it  was 
twenty-five  years  ago? 

The  most  striking  cases  of  acquired  immunity  are  for 
smallpox,  typhoid  fever,  diphtheria,  hydrophobia  or  rabies, 
and  anthrax,  a  disease  of  animals.  ^  Efforts  are  being  made 
to  develop  acquired  immunity  from  other  diseases,  and 
considerable  success  has  been  obtained  in  the  treatment  of 
tetanus  or  lockjaw,  boils  and  carbuncles,  meningitis  and 
plague. 

(a)  Vaccination  against  smallpox.  —  Over  a  hundred 
years  ago,  Edward  Jenner,  an  English  physician,  observed 
that  dairymaids  were  not  subject  to  smallpox,  which  at  that 
time  was  a  very  common  disease.  His  experiments  based 
on  this  observation  have  led  to  the  practice  of  vaccination  to 
develop  immunity  from  smallpox.  Cattle  may  have  a  disease 
known  as  cowpox,  during  which  small  sores  appear  on  the 
animals.  These  sores  contain  the  germs  of  the  disease. 
Jenner  found  that  by  scratching  the  arm  of  a  person  and 
rubbing  into  the  slight  wound  some  material  from  these 
sores  on  cattle,  a  mild  disease,  cowpox,  was  developed  in 
the  person  thus  vaccinated.  During  the  process  of  the 
disease,  something,  evidently  developed  in  the  blood  which 
protected  the  person  from  smallpox. 

Since  vaccination  has  been  practiced,  smallpox,  previously 
one  of  the  most  common  diseases,  has  become  a  very  rare 
one,  developing  only  when  vaccination  is  neglected.  Stricter 
regulations  by  boards  of  health,  especially  in  regard  to  isola- 
tion of  patients,  has  helped  materially  in  bringing  about  this 
result.  Formerly,  when  not  so  great  care  was  taken  as  now 
to  insure  the  purity  of  the  vaccine,  infection  occasionally 
occurred  from  other  germs  introduced  into  the  wound.  This 
has  now  been  obviated,  and  anyone  who  objects  to  vaccina- 


TO  PROTECT  OURSELVES  AGAINST  MICROORGANISMS       117 

tion  is  unwilling  to  perform  his  part  as  a  good  citizen  to 
maintain  the  health  of  the  community. 

(b)  Vaccination    against   typhoid  fever.  —  Vaccination   in 
this  case  is  performed  by  injecting  into  the  body  a  large 
number    of   dead    typhoid   fever   bacteria.     Usually    three 
injections  are  given  at  intervals  of  several  days.     Typhoid 
fever  up  to  recent  times  has  been  the  special  scourge  of 
army  camps.     The  value  of  anti-typhoid  vaccination  may 
be  appreciated  if  we  compare  the  prevalence  of  the  disease 
in  the  army  before  and  after  vaccination  was  practiced. 

In  the  Franco-Prussian  War,  60  per  cent  of  the  total 
German  mortality  was  due  to  this  disease.  In  the  Spanish- 
American  War  the  army  of  the  United  States  consisting  of 
107,973  men  had  20,738  cases  of  typhoid  fever  and  1580 
deaths  from  the  disease.  During  the  summer  of  1911,  after 
the  adoption  of  anti-typhoid  vaccination  by  our  govern- 
ment, an  army  division  of  over  12,000  men  was  encamped 
at  San  Antonio,  Texas,  for  about  four  months.  Among  these 
men  only  one  case  of  typhoid  fever  developed  and  that  was 
of  a  soldier  who  had  not  completed  the  necessary  inocula- 
tion. In  the  armies  of  the  Great  War,  typhoid  fever  was 
an  almost  unknown  disease. 

(c)  Immunity  from  diphtheria.  —  The  antitoxin  which  has 
curative  as  well  as  immunizing  power  against  diphtheria  is 
made  in  the  following  manner.     The  bacteria  are  permitted 
to  develop  in  a  culture  medium  until  a  considerable  quantity 
of  toxin,  or  the  poison  produced  by  the  germ,  is  present. 
After  all  the  living  germs  have  been  killed,  a  small  amount 
of  the  toxin  is  injected  into  a  healthy  horse.     The  toxin 
evidently  stimulates  the  blood  of  the  horse  to  manufacture 
something  called   antitoxin  which   counteracts  the  poison 
so  that  the  later  injection  of  toxin  may  be  greater  in  amount 


118 


GENERAL   SCIENCE 


without  injury  to  the  horse.  This  process  is  continued 
until  the  amount  of  toxin  injected  into  the  horse  is  several 
hundred  times  as  much  as  would  have  killed  it  at  the  begin- 
ning. 

A  certain  amount  of  the  blood  which  contains  great  quan- 
tities of  antitoxin  is  now  removed  from  a  large  vein  in  the 
neck  of  the  horse.  (All  this  is  done  without  pain  or  injury 
to  the  animal.)  The  serum  which  separates  from  the 
blood  when  it  clots  contains  the  antitoxin.  This  serum 


s§ 

55 

IllltlilllltttltltlUmimt 

I 

;; 

\ 

m 

i 

\ 

^ 

V 

^ 

•  • 

\ 

-.- 
^ 

^ 

b 

^ 

9 

• 

\ 

- 

V 

0 

| 

~~ 

— 

_  !l 

FIGURE  87.  —  RESULTS  OF  USE  OF  DIPHTHERIA  ANTITOXIN. 

Chart  showing  death  rate  per  10,000  from  diphtheria  before  and  after 

the  introduction  of  antitoxin. 

is  tested  for  the  amount  of  antitoxin  it  contains,  is  sterilized, 
and  put  into  vials  ready  for  use  by  physicians. 

The  accompanying  chart  shows  the  effect  of  the  use  of 
antitoxin  upon  the  death  rate  from  diphtheria  in  New  York 
City  (Figure  87). 

Antitoxin  is  of  greater  use  as  a  curative  than  as  an 
immunizing  agent.  Persons  who  have  been  exposed  to 
diphtheria  will  be  protected  only  from  two  to  six  weeks,  but 
this  is  usually  long  enough  to  protect  the  members  of  a 
family  in  which  there  is  a  case  of  the  disease.  As  a  cure  for 
diphtheria,  it  is  most  important  that  the  antitoxin  be  given 


TO  PROTECT  OURSELVES  AGAINST  MICROORGANISMS      119 


at  a  very  early  stage  of  the  disease.    The  importance  of 
this  is  shown  by  Figure  88. 

(d)  Pasteur  treatment  for  hydrophobia  or  rabies.  —  This 
disease  especially  affects  the  nervous  system.  Pasteur,  a 
noted  French  scientist,  found  that  while  the  spinal  cord  of 
a  rabbit  having  the  disease  contains  a  large  amount  of  the 
poison  of  the  disease,  the  virulence  or  power  of  the  poison 
decreases  if  the  spinal  cord  is  removed  from  the  rabbit  and 
allowed  to  dry.  As  the  disease  does  not 
develop  for  some  time  after  a  person  is 
bitten  by  a  mad  dog,  there  is  sufficient 
time  for  treatment.  The  treatment  con- 
sists in  the  injection  of  material  from  a 
rabbit's  spinal  cord  which  has  been  per- 
mitted to  dry  until  the  poison  has  almost 
entirely  disappeared.  This  is  followed 
by  injections,  more  and  more  virulent,  FIGURE  38.  —  DAN- 
of  spinal  cord  material  for  a  period  of  °ER  OFA  DELAY  IN 

r  USING  ANTITOXIN. 

about  three  weeks.  In  thousands  of  Numbers  at  the  ieft 
cases  which  have  been  treated  by  this  indicate  the  percent- 
method  there  has  been  a  mortality  of 
less  than  one  per  cent.  Just  as  in  the 
case  of  the  use  of  antitoxin  for  treatment  of  diphtheria, 
this  treatment  should  be  begun  at  the  earliest  possible  time 
after  infection  has  occurred. 


age  of  the  cases  that 
result  in  death. 


Problem    5.    Use    of    disinfectants    and    antiseptics.  — 

Certain  substances  are  used  to  prevent  the  growth  of  bac- 
teria. Make  a  list  of  substances  that  you  know  are  used 
for  this  purpose. 

The  way  in  which  they  affect  the  growth  of  bacteria  may 
be  found  out  by  the  following  experiment. 


120  GENERAL  SCIENCE 

Experiment.  —  Into  each  of  several  test  tubes  pour  about  10  cc. 
of  unsterilized  beef  tea  culture  medium. 

To  one  add  3  cc.  of  carbolic  acid  5  %  solution. 

To  another  add  3  cc.  saturated  solution  of  boracic  (boric)  acid. 

To  another  add  3  cc.  1-1000  solution  of  mercury  bichloride. 

To  another  add  3  cc.  hydrogen  peroxide. 

To  another  add  3  cc.  tincture  of  iodine. 

To  another  add  3  cc.  formaldehyde,  4%. 

To  the  others  add  3  cc.  different  disinfectants. 

To  one  add  nothing. 

After  four  or  five  days  examine  all  the  test  tubes  and  record  the 
results. 

A  distinction  is  usually  made  between  antiseptics  and  dis- 
infectants. An  antiseptic  is  a  substance  that  will  check  or 
retard  the  growth  of  bacteria,  but  does  not  destroy  them.  A 
disinfectant,  or  germicide,  is  a  substance  that  kills  bacteria. 
Some  substances  may  be  classed  under  both  heads ;  a  strong 
solution  of  it  acting  as  a  disinfectant,  a  weak  solution  act- 
ing only  as  an  antiseptic.  Salt,  sugar,  spices,  and  vinegar 
may  be  considered  antiseptics  that  are  harmless  when  taken 
into  the  body  with  food.  With  the  exception  of  the  use  of 
one  tenth  of  one  per  cent  of  benzoate  of  soda,  other  antisep- 
tics are  not  permitted  to  be  used  for  the  preservation  of  food. 

The  more  important  germicides  are  tincture  of  iodine; 
carbolic  acid  (5  to  10  per  cent  solution) ;  mercury  bichloride 
(1  part  to  1000  or  1500  parts  of  water) ;  chloride  of  lime,  and 
formaldehyde.  These  are  all  highly  poisonous  when  swal- 
lowed, and  great  care  should  be  taken  that  they  are  not 
placed  where  they  may  accidentally  be  -used  in  this  way. 

Boracic  acid  is  a  mild  antiseptic  which  is  frequently  used  as 
an  eye  or  mouth  wash.  Hydrogen  dioxide  (peroxide),  when 
it  has  not  been  allowed  to  remain  exposed  to  the  air,  will 
destroy  germs.  It  has  the  advantage  of  being  non-poisonous, 


TO  PROTECT  OURSELVES  AGAINST  MICROORGANISMS      121 

but  it  has  the  disadvantage  of  losing  its  value  if  kept  in  a 
bottle  which  is  not  well  corked. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Proof  that  flies  may  cany  bacteria. 

2.  Demonstration  of  the  comparative  value  of  the  use  of  a  feather 
duster  and  an  oiled  cloth  in  dusting,  and  of  a  broom  and  a  vacuum 
cleaner  in  sweeping. 

REPORTS 

1.  Work  of  boards  of  health. 

2.  Dangers  from  decayed  teeth. 

3.  Transmission  of  various  diseases.  -  \ 

4.  Difference  between  the   ordinary  mosquito   and  the  malaria- 
carrying  mosquito. 

5.  Description  of  operations  that  have  been  carried  on  to  get  rid 
of  malaria-carrying  mosquitoes. 

6.  Description  of  experiments  to  prove  that  malaria  is  carried  by 
mosquitoes. 

7.  Account  of  experiments  to  prove  that  yellow  fever  is  carried  by 
mosquitoes. 

8.  The  fight  against  tuberculosis. 

9.  The  history  of  the  discovery  of  vaccination  against  smallpox. 

10.  Discovery  and  value  of  diphtheria  antitoxin. 

11.  Vaccination  against  typhoid  fever  and  its  importance. 

12.  Pasteur  and  his  discovery  of  the  treatment  for  hydrophobia. 

13.  Transmission  and  seriousness  of  hook-worm  disease. 

REFERENCES  FOR  PROJECT  X 

1.  Primer  of  Sanitation,  John  W.  Ritchie.     World  Book  Company. 

2.  Preventable  Diseases,  Woods  Hutchinson.     Houghton  Mifflin 
Company. 

3.  How  to  Live,  Fisher  and  Fisk.    Funk  and  Wagnalls. 

4.  Town  and  City,  Frances  Gulick  Jewett.     Ginn  &  Co. 

5.  A  Home-made  Fly  Trap,  International  Harvester  Company, 
Chicago. 

6.  The  Human  'Mechanism,  Hough  and  Sedgwick.     Ginn  &  Co. 

7.  House  Flies,  Farmers'  Bulletins  459  and  851.    U.  S.  Department 
of  Agriculture. 


PROJECT  XI 

TO   FIND   OUT  HOW   SOME    BACTERIA   AND    MOLDS 
ARE   USEFUL 

WE  have  found  that  bacteria  and  molds  are  a  great 
nuisance,  bringing  about  a  waste  of  food  material  and  lead- 
ing us  into  the  expenditure  of  time  and  money  to  prevent 
their  ravages.  We  have  found  also  that  almost  all  diseases 
are  caused  by  them.  Just  think  of  how  conditions  would 
be  changed  if  there  were  no  such  little  plants.  Foods 
would  not  spoil,  and  diseases  like  tuberculosis,  typhoid 
fever,  influenza,  etc.,  would  be  unknown.  It  would  seem, 
therefore,  that  the  world  might  be  a  better  place  in  which 
to  live  if  bacteria  and  molds  ceased  to  exist.  But  before 
we  come  to  this  conclusion  it  will  be  well  for  us  to  consider 
if  there  is  any  evidence  that  bacteria  and  molds  are  of 
value. 

Problem  1.  Are  bacteria  of  decay  of  any  value?  —  A 
consideration  of  the  following  facts  may  help  us  to  solve 
this  problem.  Just  as  plants  take  carbon  dioxide  from  the 
air  and  build  it  up  into  starch,  so  they  also  take  simple  sub- 
stances from  the  soil  and  build  them  up  into  complete  plant 
materials.  This  means  the  removal  from  the  soil  every 
year  by  plants  of  an  immense  amount  of  these  simple  sub- 
stances needed  by  plants.  Since  the  amount  of  these  sub- 
stances is  limited,  what  must  happen  soon  unless  in  some 
way  they  are  returned  to  the  soil  ? 

This  return  is  brought  about  by  the  action  of  bacteria  in 
causing  complex  plant  and  animal  materials  (organic  mat- 

122 


HOW  SOME  BACTERIA  AND  MOLDS  ARE   USEFUL     123 

ter)  to  decay.  By  decay  the  organic  matter  is  changed 
back  into  the  simple  substances  which  plants  use  in  growth. 
Thus  it  may  be  understood  that  the  same  matter  may  many 
times  alternately  be  built  up  into  plant  and  animal  ma- 
terial and  again  be  reduced  to  a  simple  condition. 

This  building  up  and  tearing  down  may  be  illustrated 
very  simply  by  considering  the  use  of  building  blocks  by  a 
child.  Suppose  a  child  has  two  hundred  blocks,  and  builds 
them  up  into  a  house,  then  tears  it  down  and  builds  another 
structure.  This  he  may  do  time  after  time,  using  the  "same 
blocks  over  and  over  again  in  perhaps  a  different  construc- 
tion each  time.  Plants  build  up.  Bacteria  of  decay  tear 
down.  Just  as  the  child  builds  up  and  tears  down  his  block 
houses  many  times,  so  these  processes  of  building  up  by 
plants  and  tearing  down  by  bacteria  will  go  on  as  long  as 
life  exists  upon  the  earth.  What  then  do  you  think  would 
be  the  condition  of  the  earth  in  a  few  years  if  there  were 
no  bacteria  and  molds  to  do  this  tearing  down  ? 

Problem  2.  How  bacteria  on  the  roots  of  some  plants 
may  enrich  the  soil.  —  Farmers  have  known  for  a  long  time 
that  a  crop  of  clover  will  improve  the  soil.  But  the  reason 
for  this  has  been  known  for  only  relatively  a  few  years.  It 
was  found  that  in  some  fields  clover  plants  did  not  have 
the  power  to  improve  the  soil.  A  comparison  of  the  plants 
showed  that  those  which  possessed  this  power  all  had  little 
enlargements  (called  nodules)  on  their  roots  (Figure  89). 

It  was  found  also  that  if  some  of  the  soil  from  the  field 
containing  nodule-bearing  clover  plants  was  scattered  over 
the  other  field,  the  clover  plants  in  this  field  also  de- 
veloped nodules  on  their  roots  and  gained  the  power 
to  improve  the  soil.  An  examination  of  these  nodules  led 


124 


GENERAL  SCIENCE 


to  the  discovery   that  they   contained   bacteria.     It   was 
found  then  that  the  soil  could  be  inoculated  with  a  culture 
of  these  bacteria  either  by  mixing  it  with  the  clover  seed 
before  it  was  planted  or  by  adding  it  directly  to  the  soil. 
It  has  been  found  that  the  bacteria  in  these  nodules 

have  the  power 
of  changing  the 
nitrogen-  of  the 
air,  which  cannot 
be  used  directly 
by  plants,  into  a 
form  which  may 
be  built  up  into 
the  living  matter 
of  the  plant.  All 
of  the  plants  of 
the  clover  family 
(legumes)  may 
have  these  nod- 
ules containing 
nitrogen-fixing 
bacteria.  Some 
of  the  principal 
members  of  the 
family  are  peas, 
beans,  vetches, 
and  alfalfa.  If 
the  soil  does  not 


FIGURE  89.  —  ROOTS  OF  A  BEAN  PLANT. 

The  enlargements  are  nodules  containing  nitrogen- 
fixing  bacteria. 


contain  the  proper  kind  of  bacteria,  the  nodules  will  not  be 
formed  and  these  plants  will  not  be  able  to  add  to  the 
fertility  of  the  soil. 
There  are  other  bacteria  in  the  soil,  not  associated  di- 


HOW  SOME  BACTERIA   AND  MOLDS  ARE   USEFUL      125 

rectly  with  plants  as  these  nodule-inhabiting  bacteria  are, 
and  these  other  bacteria  have  the  power,  under  certain  favor- 
able conditions,  of  making  the  nitrogen  of  the  air  usable  by 
plants. 

Problem  3.  How  bacteria  are  useful  in  other  ways.  — 
Butter  made  from  sweet  cream  lacks  the  pleasant  taste  of 
sour  cream  butter.  This  is  because  in  the  ripening  of  cream 
bacteria  have  been  growing  in  it,  and  these  produce  the 
flavor  which  we  enjoy  in  butter.  That  the  especial  bacteria 
which  produce  the  desirable  taste  may  be  present,  the  cream 
may  be  inoculated  with  a  pure  culture  or  a  starter,  such  as  a 
small  quantity  of  cream  known  to  have  developed  the  de- 
sired flavor.  Frequently  the  desirable  kinds  of  bacteria  be- 
come domesticated  in  a  dairy  and  good  butter  is  produced 
without  any  effort  on  the  part  of  the  butter  maker  to  bring 
about  their  introduction. 

Likewise  the  flavor  .of  cheese  is  produced  by  bacteria  or 
molds,  the  different  flavors  being  produced  by  different 
kinds  of  organisms.  The  ripening  of  cheese  is  a  much  more 
complicated  process  than  the  ripening  of  butter,  since  it 
depends  upon  the  successive  activity  of  different  groups 
of  bacteria  or  molds  as  well  as  upon  the  presence  at  the  right 
time  of  suitable  aroma-producing  species.  The  holes  in 
certain  cheeses  are  produced  by  gas  formed  as  a  result  of  the 
action  of  particular  bacteria. 

The  action  of  bacteria  is  important  in  the  tanning  of 
skins  for  the  production  of  leather;  in  the  curing  of  to- 
bacco ;  in  the  process  of  obtaining  linen  fiber  from  flax ;  and 
in  the  manufacture  of  vinegar.  The  "  mother  "  of  vinegar 
with  which  most  of  us  are  familiar  is  made  up  of  a  great 
mass  of  bacteria  which  have  the  power  to  change  the  alco- 


126  GENERAL  SCIENCE 

hol  of  the  wine  or  cider  into  the  vinegar  acid  (acetic  acid). 
The  action  of  these  vinegar-forming  bacteria  is  hastened 
by  free  access  of  air,  so  that  barrels  containing  cider  to  be 
changed  into  vinegar  should  be  only  partially  filled  and  an 
opening  should  be  left  in  the  top  of  the  barrel  to  admit  air. 
The  formation  of  vinegar  may  be  hastened  by  permitting 
the  cider  to  trickle  through  casks  filled  with  shavings  im- 
pregnated with  old  vinegar.  Why  ? 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Grow  clover  seed  in  soil  which  has  been  baked  and  moistened  with 
boiled  water,  and  in  ordinary  garden  soil. 

2.  Collection  of  different  roots  showing  nodules. 

3.  Manufacture  of  vinegar  from  cider. 

REPORTS 

1.  Practical  use  made  of  nitrogen-fixing  bacteria. 

2.  Importance  of  bacteria  in  manufacture  of  dairy  products. 


UNIT  II 
RELATION   OF  WATER  TO  EVERYDAY  ACTIVITIES 

PROJECT  XII 

MOISTURE   IN   THE   AIR  AND   ITS   IMPORTANCE 
TO   US 

A  NUMBER  of  problems  immediately  occur  to  us:  how 
dew,  fogs,  clouds,  and  rain  are  caused ;  why  some  parts  of 
the  earth  receive  a  much  larger  rainfall  than  other  parts; 
how  water  may  be  supplied  to  regions  of  very  little  rainfall ; 
how  moisture  gets  into  the  air,  and  the  effect  of  moisture  in 
the  air  (humidity)  upon  our  comfort. 

Problem  1.  How  dew  is  caused.  —  We  all  have  had 
the  experience  of  getting  our  feet  wet  by  walking  in  the 
grass  early  on  a  summer  morning.  This  moisture  upon 
the  grass  is  called  dew.  What  are  some  of  the  things 
that  you  know  about  dew?  Was  it  on  the  grass  during 
the  day  before  ?  About  what  time  did  it  begin  to  appear 
in  the  evening?  Have  you  ever  seen  it  on  anything  except 
grass?  Does  it  seem  to  form  to  the  same  extent  on  all 
objects  ?  If  possible  give  examples.  Does  dew  form  on  ob- 
jects in  the  house  ?  On  the  porch  ?  Is  there  approximately 
the  same  amount  of  dew  every  morning?  Does  wind 
seem  to  make  any  difference  ?  Does  it  make  any  difference 
whether  the  night  is  clear  or  cloudy?  Have  you  ever  no- 
ticed moisture  similar  to  dew  on  water  pipes  or  on  a  glass 
filled  with  cold  water  ? 

127 


128  GENERAL  SCIENCE 

The  questions  above  are  for  the  purpose  of  bringing  to 
"attention  the  facts  that  you  know  about  dew.  Do  not 
guess  at  the  answers,  as  that  would  destroy  the  value  of  the 
questions. 

Several  simple  experiments  will  enable  us  tc  understand 
something  about  how  dew  is  formed,  and  under  what  con- 
ditions. 

Experiment.  —  Take  two  large  test  tubes  or  drinking  glasses.  Into 
one  of  these  pour  some  ice  water;  into  the  other  pour  water  at  the 
room  temperature.  Set  side  by  side  and  note  results. 

Experiment.  —  Into  one  of  two  wide-mouthed  jars  pour  a  small 
quantity  of  water.  Place  the  two  jars  on  a  radiator  or  heat  slightly  with 
a  Bunsen  burner.  Suspend  for  a  few  minutes  in  each  jar  a  test  tube 
containing  ice  water.  Note  results. 

After  considering  these  two  experiments,  what  do  you 
conclude  are  the  two  conditions  necessary  for  the  forma- 
tion of  a  film  of  water  like  dew  upon  objects  ? 

Experiment.  —  Pour  a  few  drops -of  water  into  a  test  tube.  Heat  the 
test  tube  until  the  water  disappears.  Now  partially  immerse  the  test 
tube  in  a  jar  of  ice  water.  What  is  the  result  ?  What  do  you  conclude 
to  be  the  relation  between  the  temperature  of  the  air  and  its  ability  to 
hold  water  in  the  form  of  vapor,  or  gas  ? 

The  temperature  at  which  moisture  in  the  air  changes 
from  an  invisible  vapor  to  visible  drops  of  water,  is  called 
the  dew  point.  Is  the  dew  point  temperature  always  the 
same?  Why?  Why  is  it  possible  to  "see  your  breath " 
on  a  cold  day  ? 

We  are  now  able  to  arrive  at  the  explanation  of  the  con- 
ditions under  which  dew  is  formed. 

(a)  Objects  on  the  earth  cool  off  after  the  sun  sets.  What 
effect  does  this  have  upon  the  surrounding  air  ?  What  may 
result? 


MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE  TO  US      129 

(6)  Some  objects  give  off  their  heat  more  readily  than 
others,  as  for  example,  a  hatchet  left  outdoors  during  the 
night  may  have  a  very  large  amount  of  dew  on  the  metal 
part,  and  but  little  on  the  wooden  handle.  Suggest  other 
examples  that  you  have  observed. 

(c)  Clouds  act  like  a  blanket  over  the  earth,  preventing 


Photographed  ty  A.  J.  Weed. 

FIGURE  90.  —  ALTO-CUMULUS  CLOUDS. 

the  heat  from  escaping.     What  effect  will  this  have  on  the 
formation  of  dew  ? 

(d)  The  layer  of  air  next  to  the  cool  object  is  cooled  down 
to  its  dew  point.    Why  will  wind  prevent  the  formation  of 
dew? 

(e)  Since  the  dew  point  is  affected  by  the  amount  of 
moisture  in  the  air,  what  is  the  effect  of  dry  weather  on  the 
formation  of  dew? 


130 


GENERAL   SCIENCE 


(/)  What  is  the  result  when  the  dew  point  is  at  the  tem- 
perature of  freezing  or  below? 

Explain  the  following : 

(1)  The  appearance  of  steam  from  an  exhaust  pipe  or  a 
steam  whistle,  and  its  appearance  when  it  is  a  little  farther 
away  from  the  vent.  Where  does  it  go?  Hold  a  Bunsen 


FIGURE  91. 


Photographed  by  A.J.  Henry. 
UNDULATED  ALTO-CUMULUS  CLOUDS. 


burner  or  a  candle  near  the  "  visible  steam  "  escaping  from 
a  vessel,  such  as  a  tea-kettle.     Result  ? 

(2)  The  mist  produced  by  blowing  one's  breath  on  a 
mirror  or  window  glass. 

(3)  Why  growing  plants  may  be  protected  from  frost  by 
placing  canvas  or  sheets  of  paper  over  them. 

(4)  Why  the  fruit  grower  sometimes  makes  a  smudge 
(smoke)  in  the  orchard  when  frost  threatens. 

(5)  Why  gardens  in  the   valleys   are  more  likely  to  be 


MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE  TO   US      131 

affected  by  early  frosts  in  the  autumn  than  gardens  on  hill- 
sides. 

(6)  Why  the  farmer  is  much  more  afraid  of  frost  on  a 
clear  night  than  on  a  cloudy  one. 

(7)  Why  he  is  more  afraid  of  frost  on  a  quiet  night  than 
on  a  windy  one. 

Problem   2.     How   fogs   and    clouds   are    produced.  — 

(1)  Explain  the  formation  of  the  thin  layer  of  mist  which 


FIGURE  92. —  CUMULUS  CLOUDS  OVER  PACIFIC  OCEAN. 
Point  Loma,  San  Diego,  California,  late  afternoon. 

is  sometimes  seen  spread  over  a  swamp  or  valley  bottom. 
Why  does  it  disappear  as  soon  as  the  sun  begins  to  shine  ? 

(2)  Fogs  are  common  on  the  Banks  of  Newfoundland 
and  the  coast  of  Maine  whenever  the  wind  is  from  the 
south.  Farther  south,  as  far  as  Cape  Hatteras,  fogs  are 
apt  to  occur  when  the  wind  is  from  the  east.  Why  ?  (Re- 


132 


GENERAL  SCIENCE 


view  your  geography  as  to  the  relative  locations  of  the 

Gulf  Stream  and  the  Labrador  Current.) 

(3)  Suggest  an  explanation  of  the  great  fogs  which  are  so 

common  in  the  British  Isles.     (Note  that  bodies  of  land 

cool  more  rapidly  than  large  bodies  of  water.)     At  what 

time  of  the  year  do  you 
think  fogs  would  be  most 
common  in  England?  In 
all  cases  the  presence  in  the 
air  of  small  particles  of  dust 
encourages  the  formation 
of  fog.  Why?  This,  no 
doubt,  has  considerable 
effect  in  intensifying  fogs 
over  cities  such  as  London. 
Clouds  are  made  up  of  a 
collection  of  small  particles 
of  water,  floating  some  dis- 
tance above  the  earth. 
Suggest  how  the  great 
masses  of  clouds  with  hori- 
zontal bases, 


FIGURE  93.  —  RAIN  GAUGE. 

The  area  of  the  top  of  the  outer 
cylinder  (a)  is  exactly  ten  times  as 
great  as  that  of  the  inner  cylinder  (b)  ; 
c,  receiver. 


seen    on    a 

summer  day,  have  been 
formed  (Figure  92).  Re- 
fer back  to  your  study  of 
weather  and  explain  why  clouds  are  present  in  a  low  pres- 
sure area  and  not  present  in  a  high  pressure  area. 

Problem  3.  How  rain,  snow,  and  hail  are  formed.  —  In 
a  cloud  or  a  fog  the  water  particles  are  so  small  that  they 
will  remain  suspended  in  the  air  for  a  long  time.  The  small 
globules  of  water  in  a  cloud  are  either  prevented  from  fall- 


MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE  TO   US      133 

ing  below  the  base  of  the  cloud  by  upward  currents  of  air, 
or  by  passing  into  a  part  of  the  air  where  the  conditions  of 
temperature  and  moisture  are  such  that  the  globules .  of 
water  will  be  changed  back  into  invisible  water  vapor. 

As  the  amount  of  water,  however,  in  a  cloud  increases  by 
the  changing  of  a  greater  quantity. of  vapor  into  globules 
of  water  (condensation),  the  small  globules  combine  to  form 


FIGURE  94. —  SNOWFLAKES  (enlarged  many  times). 

drops  of  water  which  fall  to  the  earth  as  rain.  The  change 
from  small  globules  to  large  drops  'may  be  illustrated  by 
the  following  experiment : 

Experiment.  —  Cover  with  a  metal  lid  a  large  beaker  glass  containing 
about  an  inch  of  water.  Gradually  heat  the  beaker  glass  with  a  Bunsen 
burner.  Note  results. 

If  the  temperature  of  the  air  at  the  time  of  condensation 
is  below  the  freezing  point,  the  moisture  crystallizes  into 
snowflakes  (Figure  94).  If  raindrops  are  frozen  into  little 


134  GENERAL  SCIENCE 

balls  in  their  passage  through  the  air,  they  become  hail- 
stones. Hail  is  usually  formed  in  summer,  and  is  probably 
caused  by  currents  of  air  carrying  the  raindrops  to  such  a 
height  that  they  are  frozen  and  sometimes  have  formed  on 
them  a  layer  of  snow.  Split  hailstones  will  frequently  show 
several  layers  of  ice  and  snow,  indicating  that  they  have 
been  carried  up  a  number  of  times  before  finally  falling 
to  the  earth. 


FIGURE  95.  —  HEAVY  FALL  OF  SNOW  IN  A  PINE  FOREST. 

Problem  4.  Reasons  for  unequal  distribution  of  rainfall. 
—  A  study  of  the  average  annual  rainfall  map  of  the  United 
States  (Figure  96)  shows  that  the  distribution  of  rainfall  is 
very  unequal,  varying  from  80  to  100  inches  per  year  in  a 
narrow  strip  along  the  ocean  in  Washington  and  Oregon  to 
less  than  5  inches  per  year  in  portions  of  Nevada,  southern 
California,  and  Arizona  (Figure  97). 


MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE  TO   US      135 


136 


GENERAL   SCIENCE 


With  maps  before  you  of  the  topography  of  the  country 
and  the  prevailing  winds,  explain  the  following  : 

(1)  The  great  rainfall  of  the  northwest  coast  of  the 
United  States.  What  is  the  prevailing  wind?  (Air  cools 
as  it  rises  along  the  side  of  a  mountain.)  Why  is  this 

rainfall  belt  so  narrow  ? 

(2)  The  small   rainfall  of 
the  great  region  just  east  of 
this  coast  area. 

(3)  The  sources  of  rainfall 
of  the  Mississippi  Valley  and 
region  east  of  it  to  the  At- 
lantic Coast. 

(4)  In  middle  and  south- 
ern California,  the  prevailing 
wind  from  December  to  May 
is  from  the  ocean,  while  dur- 
ing the  remainder  of  the  year 
it  is  from  the  land  toward  the 
ocean.     Explain  the  dry  and 
rainy  seasons  of  this  region. 


FIGURE  97.  —  LANDSCAPE  IN  AN  AL- 
MOST RAINLESS  DISTRICT  IN  ARIZONA. 


Problem  5.  How  water  is  supplied  to  dry  areas.  — 
Portions  of  the  country,  which  were  unfit  for  agriculture 
because  of  too  little  rainfall,  have  been  changed  into  good 
farming  regions  by  irrigation  (Figures  98  and  99) ;  water 
from  the  mountains  being  collected  in  large  reservoirs  and 
carried  by  flumes,  pipes,  or  cemented  ditches,  for  great 
distances,  to  where  the  water  is  needed  (Figure  100). 

The  accompanying  map  shows  the  location  of  districts 
irrigated  as  a  result  of  the  work  of  the  United  States  Rec- 
lamation Service  (Figure  101). 


MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE  TO   US      137 


FIGURE  98.  —  ARIZONA  DESERT  BEFORE  IRRIGATION. 


FIGURE  99.  —  ARIZONA  DESERT  AFTER  IRRIGATION, 


138 


GENERAL   SCIENCE 


Problem  6.  How  moisture  gets  into  the  air.  —  Evap- 
oration. —  It  is  evident  that  there  must  be  considerable 
water  in  the  air,  in  the  form  of  invisible  vapor.  It  has 
been  estimated  that  if  all  the  moisture  in  the  air  were  con- 
densed into  water,  it  would  make  a  layer  of  about  one 
inch  in  depth  over  the  entire  surface  of  the  earth.  Some 


FIGURE  100.  —  ROOSEVELT  DAM,  ARIZONA. 
A  large  dam  for  collection  of  water  for  irrigation. 

very  common  observations  will  indicate  to  us  how  this 
water  gets  into  the  air. 

(1)  What  happens  to  wet  clothes  hung  in  the  air? 

(2)  On  what  kind  of  days  do  they  dry  best  ? 

(3)  Do  they  dry  better  during  day  or  night  ? 

(4)  What  becomes  of  the  rain  puddles  that  are  formed 
on  the  streets?    Does  the  temperature  seem  to  make  any 
difference  ? 


MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE  TO  US      139 

(5)  What  happens  to  a  shallow  pan  of  water  left  stand- 
ing for  a  number  of  days  ? 


FIGURE  101.  —  MAP  SHOWING  LOCATION  OF  IRRIGATION  PROJECTS. 

(6)  What  must  be  added  to  a  balanced  aquarium  from 
time  to  time  ? 

(7)  Will  frozen  clothes,  hanging  on  a  line,  dry  ? 


140  GENERAL  SCIENCE 

(8)  What  happens  to  water  that  falls  on  soil,  as  in  a 
cultivated  garden  or  field? 

(9)  After  a  number  of  dry  days,  compare  the  moisture  of 
soil  under  a  board  or  stone  with  that  of  the  surrounding 
soil.     During  very  dry  weather  in  summer,  almost  the  only 
place  one  can  find  earthworms  is   under  boards,  logs,  or 
stones.    How  do  you  explain  this  ? 

(10)  When  barrels  are  left  empty  they  often  fall  to  pieces. 
Why? 

(11)  In    dry   weather,    farmers    sometimes    pour    water 
around  the  rims  of  the  wheels  of  their  wagons.     Why  ? 

(12)  How  do  leaves  appear  after  having  been  removed 
from  a  plant  ? 

From  these  observations  we  must  conclude  that  objects 
containing  water  give  it  off  to  the  air.  The  changing  of  the 
water  into  a  vapor  is  called  evaporation,  the  reverse  of  con- 
densation which  we  considered  in  the  formation  of  dew, 
clouds,  and  rain.  From  your  observations,  state  the  condi- 
tions which  you  think  would  affect  the  rapidity  of  evapora- 
tion. Not  only  are  objects  on  the  land  giving  off  water  in 
the  form  of  vapor,  but  also  the  surfaces  of  all  bodies  of 
water,  —  rivers,  lakes,  and  oceans.  This  water,  in  an  invisi- 
ble form  as  vapor,  is  changed  back  into  visible  forms  as 
dew,  clouds,  rain,  and  snow. 

When  water  evaporates,  substances  dissolved  in  the 
water  remain  behind.  This  may  be  illustrated  by  allow- 
ing a  vessel  of  water  in  which  has  been  dissolved  some  soda 
or  salt  to  stand  exposed  to  the  air  until  the  water  has 
evaporated.  Water  in  streams  flowing  to  the  ocean  con- 
tains some  soluble  mineral  material  taken  from  the  earth, 
through  which  the  water  has  trickled.  What  happens  to 
this  mineral  material  when  the  water  evaporates  (Fig- 


MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE  TO   US      141 


FIGURE  102.  —  RUSSIAN  SALT  FIELDS. 
Salt  is  left  after  evaporation  of  water. 

ure  102)  ?  State  in  your  own  language,  what  you  consider 
to  be  the  cause  of  the  saltness  of  the  ocean.  Endeavor  to 
find  out  why  the  Great  Salt  Lake  contains  salt  water,  and 
the  Great  Lakes,  fresh  water. 


142  GENERAL   SCIENCE 

Problem  7.  How  the  amount  of  moisture  in  the  air 
affects  our  comfort.  —  The  effect  of  the  amount  of  moisture 
in  the  air  (humidity)  upon  our  bodily  comfort  has  been  dis- 
cussed under  ventilation.  It  is  the  relative  humidity  rather 
than  the  actual  humidity  that  affects  us.  The  relative 
humidity  is  the  ratio  of  the  amount  of  water  in  the  air  to 
the  amount  which  it  can  hold  at  a  given 
temperature.  A  relative  humidity  of  50  % 
means  that  the  air  contains  one  half  of 
the  amount  of  moisture  that  it  can  hold 
at  that  temperature. 

You  will  recall  that  damp  days  either 
in  summer  or  winter  are  more  uncom- 
fortable than  dry  days  of  the  same 
temperature.  To  understand  this,  we 
must  consider  how  heat  is  lost  from  the 
body  in  winter  and  summer.  What  is 
the  chief  means 'of  loss  of  heat  from  the 
body  in  winter?  Explain  the  feeling  of 
chill  experienced  on  a  damp  day  in  winter, 
keeping  in  mind  that  moist  air  is  a  better 
conductor  of  heat  than  dry  air.  What 
is  the  principal  way  in  which  heat  is  lost 
FIGURE  103.— WET  from  the  body  in  summer  ?  Explain  now 
AND  DRY  BULB  THER-  why  we  are  more  oppressed  by  the  heat 

MOMETER.  on   a  damp  day 

The  relative  humidity  of  the  air  may  be  found  by  using 
the  wet  and  dry  bulb  thermometer  or  psychrometer  (Fig- 
ure 103).  This  consists  of  two  thermometers,  one  of  which 
has  a  piece  of  wet  muslin  around  its  bulb.  These  are  rapidly 
whirled  in  the  air.  Observations  of  the  readings  of  the  ther- 
mometers immediately  after  the  muslin  has  become  dry  will 


MOISTURE  IN  THE  AIR  AND  ITS  IMPORTANCE  TO  US     143 

show  considerable  difference.  Explain.  Tables  have  been 
prepared  which  give  the  relative  humidity  of  the  air  corre- 
sponding to  the  difference  between  the  dry  bulb  and  the  wet 
bulb  thermometers  at  the  different  degrees  of  temperature. 

Another  instrument  for  measuring  the  relative  humidity 
of  the  air  is  the  hair  hygrometer.  The  human  hair,  when 
the  oil  has  been  removed,  lengthens  with  dampness  and 
shortens  with  drying.  A  hair  prepared  in  this  way  is  at- 
tached to  a  pointer  which  is  moved  across  a  dial  as  the  hair 
changes  in  length. 

Use  is  made  of  the  fact  that  paper  or  cloth  impregnated 
with  certain  chemicals  will  change  color  as  the  relative 
humidity  becomes  greater  or  less.  A  paper  flower,  for 
example,  which  has  been  soaked  in  a  solution  of  cobalt 
chloride  and  gelatine,  will  be  violet  in  color  when  the  rela- 
tive humidity  is  high  and  blue  when  the  air  is  dry. 

REPORTS 

1.  How  railroads  fight  snow. 

2.  Origin  of  borax  and  other  salt  deposits  in  the  West. 

3.  The  salt  supply  of  the  United  States. 

REFERENCES  FOR  PROJECT  XII 

1.  Measurements  for  the  Household,  Bureau  of  Standards,  Washing- 
ton, D.  C. 

2.  Humidity ;  Its  Effect  on  Our  Health  and  Comfort,  P.  R.  Jameson. 
Taylor  Instrument  Company,  Rochester,  N.  Y.     10  cents. 

3.  The  Mountains  of  Cloudland  and  Rainfall,  P.  R.  Jameson.     Tay- 
lor Instrument  Company,  Rochester,  N.  Y.     10  cents. 

4.  Water  Wonders  Every  Child  Should  Know,  Jean  M.  Thompson. 
Doubleday,  Page  &  Co. 


PROJECT  XIII 


THE  RELATION  OF  PLANTS  TO  MOISTURE 

WE  all  know  that  there  is  a  close  relationship  between 
plants  and  moisture.  How  they  give  off  water ;  how  much 
they  give  off ;  and  how  the  water  is  obtained  are  problems 
to  be  solved. 

Problem  1.  Do  plants  give  off  moisture  ?  —  Under 
ordinary  circumstances  plants  do  not  seem  to  give  off  water 

to  the  air,  as  the  leaves  remain 
fresh  day  after  day.  What  hap- 
pens, however,  to  leaves  and 
flowers  when  they  have  been 
broken  from  the  plant?  What 
does  this  seem  to  indicate  ?  How 
may  these  leaves  and  flowers  be 
kept  from  wilting?  The  follow- 
ing experiment  will  enable  us  to 
find  out  if  growing  plants  give 
off  water. 

FIGURE  104.  —TRANSPIRATION.  Experiment.  —  Completely  cover  the 

What  is  the  source  of  the  water    Pot  .of  an  active1^  &0™*  geranium 

within  the  bell  jar  ?  or  similar  plant  with  rubber  tissue  or 

waxed   paper,  leaving  only  the  stem 

and  leaves  of  the  plant  exposed.     Cover  the  plant  with  a  dry  bell 
jar.     After  a  few  hours  observe  and  draw  conclusions  (Figure  104). 

This  process  of  giving  off  water  by  a  plant  is  called  tran- 
spiration. 

144 


THE  RELATION  OF  PLANTS   TO  MOISTURE  145 

Problem  2.    The  amount  of  water  given  off  by  plants. 

Experiment.  —  Cover  the  pot  of  an  actively  growing  geranium  or 
similar  plant  with  rubber  tissue  or  waxed  paper  as  in  the  preceding 
experiment.  Weigh  the  plant  and  its  pot.  After  the  plant  has  stood 
in  a  warm  room  or  outside  the  window  if  the  day  is  warm,  weigh  again. 
Result.  Roughly  estimate  the  area  of  the  leaves  and  calculate  the  loss 
of  water  per  square  inch  or  square  foot. 

Most  persons  are  surprised  when  they  realize  the  amount 
of  water  that  is  given  off  by  plants.  It  has  been  calcu- 
lated that  an  oak  tree  may  give  off  from  its  leaves  in  the 
five  months  from  June  to  October  about  125  tons  of  water ; 
and  that  a  grass  plot  50  by  150  feet  may,  under  favorable 
conditions,  give  off  by  transpiration  a  ton  of  water  in  a 
day.  A  single  corn  plant  was  found  to  give  off  31  pounds  of 
water  during  its  growth.  It  will  thus  be  seen  that  the  miles 
and  miles  of  vegetation  are  continually  giving  back  to  the 
air  the  water  which  has  been  deposited  on  the  earth  in  the 
form  of  rain. 

Problem  3.  How  the  root  system  of  a  plant -is  fitted  to 
find  water.  —  We  all  know  that  plants  obtain  water  from 
the  soil  by  means  of  their  roots.  Examine  the  roots  of  a 
plant  and  notice  how  they  are  fitted  to  reach  many  parts  of 
the  soil  (Figures  105  and  106).  There  is  a  very  close  re- 
lationship between  the  development  of  the  root  system  and 
the  water  supply. 

Experiment.  —  Across  the  middle  of  a  cigar  box  fasten  an  incomplete 
partition,  not  quite  reaching  the  bottom  of  the  box.  In  each  com- 
partment of  the  box,  plant  soaked  pea  seeds  in  moistened  sawdust. 
Keep  both  sides  watered  until  the  seedlings  have  begun  to  form  well- 
developed  root  systems.  Then  cease  to  water  one  side  but  continue 
to  water  the  other  side  generously.  At  the  end  of  two  weeks  carefully 
remove  the  sawdust  and  note  the  condition  and  arrangement  of  the, 
roots.  Conclusion  ? 


146 


GENERAL  SCIENCE 


In  trees  growing  under  normal  conditions  the  roots  ex- 
tend out  to  a  point  directly  under  the  outer  ends  of  the 
branches.  Why?  Alfalfa  plants  growing  in  dry  regions 
may  have  roots  extending  to  a  depth  of  10  or  12  feet.  Why  ? 
The  mesquite  plant  living  in  the  dry  regions  of  the  south- 
western part  of  the  United  States  and  Mexico,  although 
only  a  low  shrub,  may  send  its  roots  to  a  depth  of  60  feet  in 


I 


FIGURE  105.  —  UPTURNED  SUGAR  MAPLE. 
Note  the  very  large  number  of  small  roots. 

search  of  water.  Why  does  a  lawn  which  has  been  sprinkled 
for  a  short  time  every  day  look  worse  after  being  neglected 
for  a  few  dry  weeks  in  August  than  the  neighboring  lawn 
which  has  not  received  the  same  care?  Give  one  reason 
why  weeds  in  a  garden  are  harmful. 

Problem  4.    How  roots  are  especially  fitted  to  take  in 
moisture.  —  You  have  probably  noticed  that  even  though 


THE  RELATION  OF  PLANTS  TO  MOISTURE 


147 


the  greatest  care  be  taken  to  prevent  injury  to  the  roots,  a 
plant  is  apt  to  wither  and  be  checked  in  its  growth  when 
transplanted  (planted  again  after  having  been  removed 
from  soil  in  which  it  has  been  growing).  This  might  lead 
us  to  suspect  that  there  are  special  structures  on  the  roots 
which  are  injured  in 
the  process  of  trans- 
planting. 

Growing  roots  in 
such  a  way  that  they 
can  be  examined 
without  being  dis- 
turbed may  help  us 
to  find  out  if  roots 
possess  any  special 
structures. 


Experiment.  —  Place 
some  radish  seeds  or 
other  small  seeds  be- 
tween a  moist  blotter 
and  the  bottom  of  a  Petri 
dish  or  the  inside  of  a  test 
tube.  Keep  in  a  warm 
place  and  examine  after 
three  or  four  days. 
What  do  you  find? 


FIGURE  106. — YOUNG  WHITE  CEDARS. 


The  small  hairlike  structures  which  you  see  on  the  young 
root  are  called  root  hairs  (Figure  107).  Their  structure,  as 
you  will  see  from  the  diagram  (Figure  108),  is  very  simple. 
Each  hair  consists  of  a  delicate  wall  inclosing  a  thin  layer  of 
the  living  matter  of  the  plant  and  some  watery  material 
called  celLsap.  It  will  be  noticed  that  the  root  hair  is 


148 


GENERAL   SCIENCE 


only  the  extension  of  one  of  the  little  boxes  containing  living 
matter  (cells)  of  which  the  young  root  is  composed.     Of 

what  advantage  are 
these  root  hairs  ? 

Problem  5.  How 
root  hairs  take  in 
water.  —  The  way  in 
which  root  hairs  take 
in  water  is  illustrated 
by  the  following  ex- 
periment. 

Experiment.  —  Care- 
fully chip  off  about  one 
half  of  a  square  inch  of 
the  shell  from  the  blunt 
end  of  a  fresh  egg,  taking 
care  not  to  injure  the 
membrane  lying  under  the  shell.  Support  the  egg  at  the  top  of  a  glass 
containing  water  so  that  the  exposed  membrane  is  immersed  in  the 
water.  Puncture  the  shell  and  membrane  at  the  other  end  of  the  egg 
and  by  means  of  a  needle  mix  the  white  and  yolk  of  the  egg.  Into  this 
end  of  the  egg  fasten  a  glass  tube  with  sealing  wax,  clamp  the  tube  to 
an  iron  support  and  set  aside 
for  a  few  hours.  What  has 
happened  ?  Explain  how  this 
illustrates  the  work  of  the 
r°ot  hair.  Epidermal 

Liquids  separated  by 
a  plant  or  an  animal 
membrane  tend  to  mix 
with  each  other,  but  in  this  case  the  contents  of  the  egg, 
like  those  of  the  root  hair,  are  unable  to  pass  through  a 
membrane,  so  the  flow  of  liquid  is  all  in  one  direction.  At 


FIGURE  107.  —  GERMINATING  WHEAT  SHOWING 
ROOT  HAIRS. 


Nucleus 


FIGURE  108.  —  ROOT  HAIRS  (enlarged). 


THE  RELATION  OF  PLANTS   TO  MOISTURE 


149 


the  same  time  that  water  passes  into  the  root  hair,  raw 
food  material  needed  by  the  plant  also  passes  in.  The  part 
of  the  stem  through  which  the  liquids  pass  upward  may  be 
seen  by  cutting  across  a 
living  twig,  the  base  of 
which  has  been  kept  in 
red  ink  for  several  days. 

Problem  6.  How 
water  passes  out  of  the 
leaves.  —  Does  water 
pass  out  equally  well 
from  all  parts  of  the  leaf  ? 
This  question  may  be 
answered  by  the  follow- 
ing experiment : 

Experiment.  —  Remove 
several  leaves  from  a  plant. 
Cover  the  upper  surface  of 
some  of  the  leaves  and  the 
lower  surfaces  of  others  with 
a  thin  layer  of  vaseline.  Ex- 
amine after  several  hours. 
Which  leaves  have  withered 
most  ?  Conclusion  ? 

Has  the  lower  surface 
of  the  leaf  any  openings 
by  which  moisture  es- 
capes? To  answer  this 
question  examine  a  bit 
of  the  membrane  or  epidermis  stripped  from  the  lower  sur- 
face of  a  leaf  (Figure  110). 

The  kidney-shaped  cells  (guard  cells)  on  each  side  of  the 


FIGURE  109.  —  A  LIVING  TREE  WITH  A 
HOLLOW  TRUNK. 

What  does  this  indicate  as  to  the  part  of 
the  stem  through  which  liquids  pass  ? 


150 


GENERAL   SCIENCE 


openings  (stomates)  absorb,  in  moist  weather,  moisture  from 
the  air  and  swell  up  like  the  inner  tube  of  an  automobile 

tire  when  filled  with  air,  mak- 
ing the  opening  or  stomate 
large.  In  dry  weather  they 
lose  their  moisture,  collapse, 
and  make  the  stomate  smaller. 
Of  what  advantage  is  this  to 
the  plant?  Plants  that  live 
in  dry  regions  possess  various 
devices  for  the  prevention  of 


FIGURE  110.  —  LOWER  EPIDERMIS 
OF  A  LEAF  (highly  magnified). 


excessive   transpiration,    such    as    hairy,    or   thick-skinned 
leaves,  or  the  reduction  of  leaf  surface. 


SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Find  out  approximately  how  much  water  may  be  given  to  the  air 
by  a  certain  tree  during  one  hour  on  a  warm  day  in  summer. 

2.  Find  out  the  amount  of  water  given  to  the  air  by  a  geranium  plant 
in  24  hours. 

3.  Endeavor  to  find  out  the  total  extent  of  the  r'oot  system  of  some 
plant. 

4.  Construct  an  apparatus  to  illustrate  the  action  of  the  stomates. 

REPORTS 

1.  Comparison  of  the  kinds  of  plants  in  arid  regions  and  those  in  well 
watered  regions. 

2.  Importance  of  irrigation  in  the.  United  States. 

3.  Dry  farming  in  the  Western  States. 

4.  The  salt  supply  of  the  United  States. 

REFERENCES  FOR  PROJECT  XIII 

1.  Agriculture  on  Government  Reclamation  Projects,  Scofield  and 
Fairell.     U.  S.  Department  of  Agriculture  Year  Book,  1916. 

2.  Irrigation  an,d  Drainage,  F.  H.  Wing.    Macmillan  Company. 


THE  RELATION  OF  PLANTS   TO  MOISTURE  151 

3.  A  Primer  of  Forestry,  Gifford  Pinchot.     Government  Printing 
Office,  Washington,  D.  C. 

4.  First  Book  of  Forestry,  F.  Roth.     Ginn  &  Co. 

5.  Irrigation,  Farmers'  Bulletin  864.     U.  S.  Department  of  Agri- 
culture, Washington,  D.  C. 

6.  Dry  Farming,  Widtsoe.    Macmillan  Company. 


PROJECT  XIV 
WATER  POWER 

IT  is  estimated  that  if  the  water  power  of  the  United  States 
were  fully  used,  it  would  be  sufficient  to  run  all  the  machines 
of  our  factories,  to  propel  all  railroad  trains,  street  cars,  and 
automobiles,  and  to  furnish  light  and  heat  for  the  many 


FIGURE  111. — TRAIN  DRAWN  BY  AN  ELECTRIC  LOCOMOTIVE. 
The  power  of  this  electric  locomotive  is  derived  from  water  power. 

purposes  for  which  they  are  used  (Figure  111).  At  present 
only  a  small  part  of  this  power  is  being  used,  but  the  possi- 
bilities for  the  future  are  great  (Figure  112).  The  ques- 
tions that  arise  in  our  minds  naturally  are:  What  is  the 
source  of  the  energy  or  power  of  water  power  and  where 

152 


WATER  POWER  153 

and  how  can  water  power  be  best  developed.  Another 
problem  somewhat  associated  in  our  minds  with  water 
power  is  the  advantage  gained  by  the  use  of  hydraulic 
pressure. 

Problem  1.  What  is  the  source  of  energy  of  water  power  ? 
—  What  is  the  source  of  this  energy  which  may  be  used  in 
running  water  wheels  or  turbines,  whose  energy  in  turn  may 


FIGURE  112. —  WATERFALL,  MCKENZIE  RIVER,  OREGON. 
Sufficient  unused  power  to  light  a  city. 

be  transformed  into  heat,  light,  electrical  and  mechanical 
energy  (Figure  113)?  We  know  that  falling  bodies  exert 
energy,  but  no  more  than  is  put  into  them  in  raising  them  to 
the  point  from  which  they  fall.  The  pile  driver  exerts  en- 
ergy in  driving  piles  into  the  earth,  but  an  engine  must  be 
used  to  pull  the  weight  up  to  the  place  from  which  it  is 
dropped. 

In  country  houses,  running  water  is  frequently  supplied 


154 


GENERAL  SCIENCE 


from  an  elevated  tank.  The  energy  possessed  by  the  run- 
ning water  may  be  demonstrated  by  permitting  it  to  run 
a  water  motor,  which  in  turn  may  run  a  sewing  machine, 
a  churn,  or  a  washing  machine.  Energy,  however,  usually 
supplied  by  a  windmill  or  the  burning  of  fuel  in  an  engine 
must  be  used  to  pump  the  water  into  the  tank.  Thus  the 


POWER  HOUSE 


FIGURE  113.  —  DIAGRAM  OF  A  POWER  HOUSE. 

Water  passing  through  A  turns  the  water  wheel  B.    At  D  the  energy  of 
motion  is  changed  by  a  dynamo  into  electrical  energy. 

energy  set  free  by  the  windmill  or  by  the  burning  of  the  fuel 
is  transformed  into  the  energy  possessed  by  the  water  because 
of  its  position.  We  can  understand  now,,  that  energy,  or  the 
power  of  doing  work,  exhibited  by  water  in  rivers  and  streams 
on  their  way  to  the  ocean,  must  have  been  given  to  it  in  some 
way.  The  following  suggestions  may  lead  you  to  an  under- 
standing of  the  source  of  the  energy-  of  water  power : 


WATER  POWER  155 

(a)  What  was  the  original  location  of  the  water  concerned  ? 
(6)  What  is  happening  to  water  on  the  surface  of  oceans 
and  lakes? 

(c)  What  is  the  relation  of  evaporation  to  heat? 

(d)  What  is  the  source  of  the  heat  used  up  in  changing  the 
water  into  invisible  water  vapor,  a  gas  ? 

(e)  Just  as  steam,  which  is  invisible  water  vapor,  possesses 
energy,  so  this  water  vapor  which  results  from  the  ordinary 
evaporation  of  water  by  the  sun's  rays  has  been  given  the 
energy  which  was  used  in  changing  the  water  into  vapor. 

(/)  Because  of  the  energy  which  it  possesses,  the  water 
rapor  is  able  to  overcome  the  force  of  gravity  (the  force 
which  draws  things  to  the  earth)  and  to  move  away  from  the 
surface.  It  is  assisted  in  its  movement  by  the  currents  of 
air  and  winds,  which  you  will  recall,  are  caused  by  the  heat 
of  the  sun. 

(g)  When  condensed  into  drops  of  water,  the  energy  which 
the  vapor  possessed  as  a  gas  is  changed  largely  into  energy 
of  position  which  is  changed  into  the  energy  of  water  power, 
as  the  water  travels  in  streams  toward  the  ocean  again. 

In  your  own  language,  explain  how  water  power  depends 
upon  the  energy  of  the  sun. 

The  energy  of  the  water  power  developed  at  Niagara  Falls, 
from  the  Mississippi  River  at  Keokuk,  Iowa,  and  in  the 
streams  which  flow  from  the  higher  regions  of  the  Appala- 
chian Mountains,  upper  portions  of  the  Great  Lakes  region, 
and  the  Rocky  and  Sierra  Mountains,  can  be  changed  into 
electrical  energy  and  be  transmitted  many  miles  to  cities 
where  it  may  be  used  to  run  mills  and  trains,  and  to  furnish 
light  and  heat  (Figure  114). 

In  order  to  make  use  of  the  water  power  of  a  river  in  which 
there  are  no  falls  but  only  a  gradual  slope  of  the  river  bed, 


156. 


GENERAL   SCIENCE 


dams  are  built  which  raise  the  surface  to  a  higher  level. 
(Figure  115).  By  this  means  artificial  falls  are  produced 
which  may  represent  the  natural  fall  of  the  river  for  several 


HI 

FIGURE  114.  —  ELECTRIC  HIGH  TENSION  TRANSMISSION  LINE. 

By  these  wires  electric  power  developed  by  a  waterfall  in  the  mountains  is 

carried  to  cities  many  miles  away. 

miles  above  the  location  of  the  mill  or  factory  which  is  run 
by  its  power.  Thus  we  may  understand  how  water  power 
can  be  developed  from  any  stream  in  which  there  is  an  ap- 


WATER  POWER  .  157 

preciable  current.  Even  in  parts  of  the  country  which  are 
relatively  level,  the  mill  dams  from  which  power  is  de- 
veloped to  run  flour  or  saw  mills  are  common.  With  the 


FIGURE  115.  —  WATER  POWER.  STATION. 

great  demand  for  electricity  there  is  need  for  the  larger  de- 
velopment of  this  source  of  power. 

Problem  2.  Source  of  the  power  of  hydraulic  pressure.  — 
Hydraulic  pressure  which  is  used  in  barbers'  chairs,  in  some 
kinds  of  elevators,  and  in  various  mechanical 
operations  to  produce  great  pressure,  may  be 
considered  a  form  of  water  power.  The  follow- 
ing experiment  may  help  us  to  understand  how 
the  great  power  of  hydraulic  pressure  is  ob- 
tained. 

Experiment. — Fill  a  bottle  with  water.  Into  the 
mouth  of  the  bottle  fit  a  perforated  stopper  which  must 
be  wired  in  or  fastened  by  the  device  represented 
in  the  figure.  Fit  tightly  into  the  opening  in  the  FIGURE  116. 


158 


GENERAL  SCIENCE 


stopper  a  metal  rod   (Figure  116).     Push  down  on  the  metal  rod. 
What  happens? 

It  is  evident  from  this  experiment  that  the  force  exerted  on 
the  inner  surface  of  the  bottle  is  many  times  the  force  exerted 
on  the  metal  rod.  This  and  other  experiments  show  that 
the  pressure  on  liquid,  as  water,  inclosed  in  a  vessel  is  trans- 
mitted undiminished  in  every  direction  and  acts  with  equal 
force  on  all  surfaces  of  equal  area.  This  is  known  as  Pascal's 

principle  since  it  was  first  an- 
nounced by  Pascal,  a  Frenchman, 
in  1653.  How  the  great  force 
exerted  by  the  hydraulic  press  is 
gained  may  be  understood  by  study- 
ing the  accompanying  diagram 
which  shows  how  a  1 -pound  weight 
may  balance  a  pressure  of  100 
pounds.  In  commercial  hydraulic 
presses,  oil  is  generally  used  in- 
stead of  water. 

By  pushing  down  the  small  pis- 
ton, a  small  amount  of  oil  is  forced 
into  the  space  below  the  large  pis- 
ton. The  force  exerted  upon  the  large  piston  is  as  many 
times  greater  than  the  force  exerted  upon  the  small  one  as 
the  surface  of  the  large  piston  is  greater  than  the  surface  of 
the  small  one.  A  valve  prevents  the  oil  from  passing  out 
of  the  cylinder  below  the  large  piston. 

Because  of  the  great  force  exerted  by  the  hydraulic 
press  it  is  used  in  lifting  heavy  weights  and  in  operations 
where  great  pressure  is  needed.  Heavy  machinery  and 
crucibles  filled  with  molten  metal  may  be  lifted  with  ease. 
Baling  of  cotton  and  paper,  punching  holes  in  steel  plates, 


FIGURE  117.  —  HYDRAULIC 
PRESS. 

A ,  large  cylinder ;  B,  small 
cylinder ;  C,  connecting  tube ; 
P,  large  piston;  p,  small 
piston  ;  D,  reservoir  for  liquid. 


WATER  POWER  159 

making  pressed  steel  and  forcing  lead  through  a  die  in  the 
manufacture  of  lead  pipe  are  some  of  the  uses  made  of  the 
enormous  force  exerted  by  the  hydraulic  press. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Construct  a  water  wheel  which  when  operated  by  water  from 
a  faucet  will  run  a  simple  machine. 

2.  Demonstration  of  the  structure  and  action  of  a  water  motor. 

3.  Make  a  small  hydraulic  press. 

4.  Construct  a  map  of  the  United  States,  and  indicate  in  red  the 
places  where  water  power  is  utilized,  and  in  blue  other  places  where 
you  think  it  might  be  used  to  advantage. 

REPORTS 

1.  Utilization  of  the  water  power  of  Niagara  Falls. 

2.  Water  power  development  in  different  parts  of  the  United  States. 

REFERENCES  FOR  PROJECT  XIV 

1.  How  It  Is  Done,  A.  Williams.     Thos.  Nelson  &  Sons.     (Power 
from  Niagara  Falls.) 

2.  Harper's  Machinery  Book  for  Boys,  Adams.     Harper  &  Bros. 
(Water-Power. ) 

3.  Practical  Things  with  Simple  Tools,  Goldsmith.     Sully  &  Klein- 
teich.     (Making  of  Water  Wheels.) 

4.  All  about  Engineering,  Knox.     Funk  &  Wagnalls.     (Niagara 
etc.) 


PROJECT  XV 

TO  UNDERSTAND   HOW  COMMUNITIES   OBTAIN  A 
GOOD   SUPPLY   OF   WATER 

Water  Supply  of  New  York  City.  —  The  average  daily 
consumption  of  water  in  New  York  City  during  the  year 
1917  was  almost  600,000,000  gallons  or  80,000,000  cubic 
feet.  Naturally  the  question  arises  how  such  an  enormous 
quantity  of  water  can  be  supplied.  Cities  like  Chicago, 
Cleveland,  or  Buffalo  may  get  their  supply  from  the  great 
fresh-water  lakes  near  which  they  are  located.  New  York, 
however,  is  shut  off  from  such  a  supply.  When  a  small 
city,  it  depended  largely  upon  wells ;  but  as  the  population 
increased,  such  a  supply  became  both  inadequate  and  un- 
safe because  of  the  danger  of  pollution.  Beginning  in  1842, 
water  of  the  Croton  watershed,  an  area  of  375  square  miles, 
about  22  miles  north  of  the  city,  was  collected  in  a  number 
of  reservoirs  and  lakes,  and  carried  to  the  city  by  the  Croton 
aqueduct. 

With  the  enormous  growth  of  population,  even  this  great 
supply  was  found  to  be  insufficient ;  and  the  city  has  ob- 
tained control  of  a  large  area  of  land  in  the  Catskill  Moun- 
tains, extending  between  75  and  125  miles  from  New  York. 
With  the  expenditure  of  about  $200,000,000  there  has  been 
developed  a  water  supply  system  which  for  many  years  to 
come  will  be  able  to  furnish  the  city  with  the  enormous 
quantity  which  it  needs  (Figure  118). 

160 


HOW  COMMUNITIES  OBTAIN  A  GOOD   WATER  SUPPLY      161 


Problem  1.  Why  a  wooded  mountainous  region  is 
selected  to  furnish  water.  —  You  will  notice  that  a  wooded 
mountainous  region  has  been  selected  as  the  water  supply 
area.  If  the  popu- 
lation of  the  city 
should  increase  to 
such  an  extent  that 
the  Croton  and  the 
Catskill  regions  would 
not  furnish  a  suffi- 
cient supply  of  water, 
there  is  still  the  great 
Adirondack  supply  to 
be  tapped.  The  ad- 
vantages of  selecting 
such  a  region  may  be 
understood  from  a 
consideration  of  the 
following  questions: 

(a)  From  what  di- 
rection do  the  moist 
winds  of  the  eastern 
part    of    New    York 
State  come? 

(b)  What     is     the 
effect  of   the   moun- 


these 


FIGURE    118.  —  SOURCE  OF  WATER  SUPPLY  OF 
NEW  YORK  CITY. 


tains    upon 
winds  ? 

(c)  Compare  the  agriculture  of  the  mountains  and  the 
level  country.  How  does  this  affect  (a)  the  cost  of  acquiring 
the  land,  (b)  the  removal  from  cultivation  of  crop-producing 
land,  and  (c)  danger  from  pollution? 


162 


GENERAL   SCIENCE 


FIGURE  1 19.  —  KENSICO  DAM. 

This  is  one  of  the  greatest  masonry  structures  in  the  world.  It  rises  307 
feet  above  the  rock  foundation  upon  which  it  rests.  .  Its  thickness  at  its 
b,ase  is  233  feet. 

(d)  Of  what  importance  is  the  elevation  of  the  source  of 
supply  to  the  water  pressure  in  the  pipes  in  the  city?    The 


FIGURE  120.  —  HEIGHT  TO  WHICH  NEW  YORK  WATER  WILL  RISE  WITHOUT 
BEING  PUMPED. 


HOW  COMMUNITIES  OBTAIN  A  GOOD   WATER  SUPPLY      163 

water  surface  of  the  chief  reservoir  (Ashokan)  of  the  Catskill 
system  is  590  feet  above  sea  level.  Because  water  seeks  its 
level,  there  is  sufficient  pressure  to  raise  it  to  all  floors  of 
buildings  of  reasonable  height,  about  260  feet,  without 
the  use  of  pumps  (Figure  120).  It  is  estimated  that  this 
has  saved  an  expense  of  $2,000,000  per  year  since  the  use  of 
the  Catskill  supply  began. 

(e)  Does  the  fact  that  the  mountains  are  covered  with 
forests  make  any  difference?     The  floor  of  the  forest,  made 


URE  121.  —  FOREST  FLOOR. 


up  largely  of  decayed  leaves  and  interlacing  roots,  acts  as 
a  great  sponge  (Figure  121).  What  effect  will  this  have  at 
seasons  of  heavy  rainfall  ?  On  the  other  hand,  during  dry 
weather  the  water  which  has  been  absorbed  by  the  forest  bed 
is  gradually  being  given  off,  usually  in  the  form  of  springs, 


164  GENERAL  SCIENCE 

to   the   small   streams  which   carry  it  into   the   collecting 
reservoirs  (Figure  122). 

Problem  2.  How  the  water  is  protected.  —  The  facts 
(1)  that  the  people  of  New  York  City  drink  water  drawn 
directly  from  the  mains,  and  (2)  that  for  many  years  there 
have  been  no  epidemics  caused  by  polluted  water,  lead  us 
to  wonder  what  precautions  are  taken  to  keep  the  supply 


FIGURE  122. — A  STREAM  IN  THE  CATSKILL  MOUNTAINS. 

This  is  one  of  the  feeders  of  the  Ashokan  reservoir  of  the  New  York  City 
Water  Supply. 

pure,  when  we  remember  1;hat  the  drinking  of  unboiled  water 
from  a  stream  is  often  very  dangerous,  and  that  the  reser- 
voirs are  supplied  largely  by  small  streams. 

We  have  already  found  that  water  in  mountains  is  less  apt 
to  contain  disease  germs.  Explain  again  the  reason  for  this. 
A  number  of  special  precautions,  however,  have  been  taken 
to  insure  the  purity  of  the  water. 


HOW  COMMUNITIES  OBTAIN  A  GOOD   WATER  SUPPLY     165 

(a)  In  order  to  keep  settlements  at  a  reasonable  distance 
from  the  shores  of  the  Ashokan  reservoir,  the  city  has  taken 
enough  land  to  afford  a  marginal  strip  of  at  least  1000  feet 
wide  around  the  shore.  Explain  the  advantage  of  this. 

(6)  The  reservoirs  act  as  great  settling  tanks.  Particles 
of  dirt  which  have  been  carried  into  the  reservoirs  sink  to 
the  bottom,  carrying  with  them  the  bacteria  which  may  be 


FIGURE  123.  —  AERATORS. 

Aeration  of  water  before  it  passes  into  the  great  pipe  that  carries  it  to 
the  City. 

attached  to  them.  Experiments  have  shown  that  prac- 
tically no  pathogenic  bacteria  will  long  survive  under  these 
conditions.  Exposure  of  the  water  in  the  storage  reservoirs 
to  sunlight  and  air  also  assists  in  the  destruction  of  any 
injurious  germs  that  may  be  present. 

(c)  At  the  Ashokan  and  Kensico  reservoirs  aerators  have 
been  built  (Figure  123).  These  consist  of  large  numbers  of 
nozzles  through  which  jets  of  water  are  thrown  into  the  air 


166 


GENERAL  SCIENCE 


as  in  a  fountain.  Not  only  do  the  oxygen  of  the  air  and 
the  sunlight  help  to  destroy  bacteria,  but  unpleasant  tastes 
and  odors  are  removed  and  the  water  made  much  more 
palatable.  The  effect  of  aeration  of  water  upon  its  palata- 
bility  may  be  tested  by  first  drinking  some  boiled  water, 
and  then  drinking  some  which  has  been  poured  several  times 
in  a  thin  stream  from  one  vessel  to  another. 

(d)  In  addition  to  what  may  be  called  the  natural  agencies 
at  work  to  make  the  water  pure,  chlorine  gas  (a  very  powerful 
sterilizing  agent)  is  introduced  into  it  just  below  the  Kensico 
reservoir,  if  the  bacteriological  examination  of  the  water 


FIGURE  124.  —  DIAGRAM  OF  A  CITY  WATER  SUPPLY  SYSTEM. 

Note  pumping  station,  stand  pipe,  water  supply  for  houses,  fountain  and 
fire  prevention. 

indicates  the  need  for  this  treatment.  The  gas  is  wholly 
neutralized  or  dissipated  before  the  water  reaches  the  dis- 
tribution pipes  of  the  city. 

Problem  3.  How  other  cities  obtain  a  supply  of  water.  — 
Every  large  city  has  special  problems  to  work  out  in  con- 
nection with  its  water  supply  system.  Many  depend  upon 
the  collected  rainfall  from  an  area  more  or  less  controlled 
by  the  city,  as  New  York  does.  Some  depend  partly  upon 
artesian  wells,  which  tap  layers  of  porous  rock  that  come  to 
the  surface  sometimes  hundreds  of  miles  away  and  absorb 
much  of  the  -rainfall  of  that  region.  Others  depend  directly 


HOW  COMMUNITIES  OBTAIN  A  GOOD   WATER  SUPPLY      167 

upon  river  water  which  is  purified  by  chlorination  and  the 
passage  through  great  filters  which  remove  much  of  the 
suspended  matter.  Still  others  may  obtain  water  directly 
from  large  bodies  of  fresh  water  as  do  the  cities  on  the  Great 
Lakes. 

Make  a  list  of  the  uses  of  water  in  your  community. 
What  do  you  know  concerning  its  water  supply? 


FIGURE  125.  —  RESERVOIR  AND  DAM. 
A  part  of  the  water  supply  system  of  Denver,  Colorado. 

Pupils  should  work  out  carefully  the  water  supply  of  their 
own  community,  finding  out  the  source  of  the  water,  means 
taken  to  protect  its  purity,  and  how  it  is  carried  to  the 
consumer. 

Rural  water  supply.  —  Villages  and  individual  homes  in 
the  country  frequently  depend  upon  relatively  shallow  wells, 
the  water  of  which  is  of  course  supplied  by  that  portion 
of  the  rainfall  which  has  soaked  into  the  earth.  Great  care 


168 


GENERAL  SCIENCE 


should  be  taken  as  to  the  location  of  such  wells,  and  their 
protection  from  surface  water. 

In  many  cases,  deeper  wells  which  penetrate  layers  of  clay 
or  even  rock  are  depended  upon.  The  water  of  such  wells 
frequently  has  minerals  dissolved  in  it.  Why?  The 
water  from  wells  in  a  limestone  region  will  not  form  a  lather 
with  soap  and  is  called  "  hard."  Thie  is  due  to  the  power  of 

water  to  dissolve  lime- 
stone. Illustration  of 
this  may  be  seen  in 
any  cemetery  where 
there  are  old  marble 
tombstones.  What  is 
the  condition  of  the 
inscriptions  on  the 
stones?  In  some 
parts  of  the  country, 
especially  in  Ken- 
tucky, Virginia,  and 
Indiana,  underground 
waters  have  dissolved 
away  the  rock  to  such 
an  extent  that  large 
caves  have  been 
formed  (Figure  126). 
Notable  among  these  are  Mammoth  Cave  of  Kentucky  and 
Luray  Cave  of  Virginia.  A  tea-kettle  in  which  "  hard  " 
water  is  used  becomes  incrusted  on  the  inside  with  a 
grayish  deposit  which  is  really  limestone. 

Problem  4.  How  the  water  system  within  the  house 
should  be  cared  for.  —  The  water  pipes  in  our  homes  are, 


FIGURE  126.  —  LIMESTONE  CAVE. 

Dissolved  out  by  water.  The  projections 
from  the  roof  were  formed  by  deposits  of 
particles  of  limestone  from  water  trickling  into 
the  cave. 


HOW  COMMUNITIES  OBTAIN  A   GOOD   WATER  SUPPLY      1(39 


of  course,  direct  continuations  of  the  main  pipes.  What 
causes  the  water  to  flow  out  when  we  open  a  tap  ?  Providing 
that  there  are  no  leaks,  we  need  give  the  pipes  very  little 
attention.  For  convenience  in  repairing  the  pipes  and 
faucets,  there  should  be  various  places  where  the  water  may 
be  shut  off,  and  outlets  by  which  the  pipes  may  be  emptied. 
In  your  own  home  locate  these  places. 

Probably  no  part  of  the  water  system  causes  so  much 
annoyance  as  the  tank  of  the  water  closet.  The  work- 
ing of  one  kind  in  general  use 
is  illustrated  by  the  diagram 
(Figure  127).  From  the  dia- 
gram explain  how  it  works. 
Examine  the  way  the  tank  in 
the  water  closet  in  your  home 
is  emptied  and  filled. 

In  winter  there  is  danger  of 
the  water  freezing  in  the  pipes; 
and  as  water  expands  in  freez- 
ing, the  pipes  often  burst.  This 


FIGURE  127. — WATER  CLOSET 

TANK. 

How  does  the  water  pass  out  ot 
the  tank  ?     Notice  the  relation  ox 


may  usually  be   prevented   by  J^JS  £££**•* 

allowing  the  water  to  drip  from 

the  faucets  on  a  cold  night.  Moving  water  does  not  freeze 
so  rapidly  as  quiet  water,  as  you  know  from  observing 
the  differing  rapidity  with  which  ponds  and  streams  freeze. 
If  a  house  is  to  be  left  vacant  during  the  winter,  the  water 
should  be  drained  from  the  pipes,  and  if  there  are  portions 
from  which  the  water  cannot  be  removed  in  this  way,  a 
plumber  should  be  engaged  to  "  blow  out "  the  pipes  by 
forcing  air  through  them. 


170  GENERAL  SCIENCE 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Construct  a  model  of  the  water  system  of  your  community. 

2.  Determine  the  source  of  water  of  any  springs  in  your  vicinity. 

3.  Make  a  plan  of  water  pipes  in  your  house.     Explain  the  advan- 
tage of  this  arrangement.     In  what  way  could  the  arrangement  have 
been  improved  ?    Explain. 

4.  Demonstrate  the  structure  of  a  faucet.     Show  how  it  may  get 
out  of  order  and  what  may  be  done  to  correct  the  trouble. 

5.  Study  out  the  mechanism  in  the  tank  of  the  toilet  in  your  home. 
Where  is  it  apt  to  get  out  of  order,  and  how  may  this  condition  be 
corrected? 

REPORTS 

1.  Describe  the  methods  used  by  a  number  of  large  cities  to  obtain 
a  good  water  supply. 

2.  Tell  how  the  American  army  was  supplied  with  pure  water  in 

France; 

\  , 

REFERENCES  FOR  PROJECT  XV 

1.  Home  Water  Works,  C.  J.  Lynde.    Sturgis. 

2.  Water  Works  in  38  Cities  in  Iowa,  John  H.  Dunlap.     Univer- 
sity Extension  Division,  University  of  Iowa,  Iowa  City,  Iowa,  5  cents. 

3.  Low  Cost  Farm  Water  Works,  Conference  for  Education  in  the 
South.     508  McLachlen  Building,  Washington,  D.  C. 

4.  Drinking  Water  and  Ice  Supplies  and  Their  Relations  to  Health 
and  Disease,  T.  M.  Prudden.    Putnam. 


PROJECT  XVI 


TO  UNDERSTAND   THE  DISPOSAL   OF  SEWAGE  OF 
HOMES  AND   COMMUNITIES 

THE  problem  of  getting  rid  of  the  waste  of  the  home  and 
of  the  community  is  almost,  if  not  equally,  as  important  as 
obtaining  a  good  water  supply.  As  in  the  case  of  the  water 
supply  its  importance  increases  as  cities  increase  in  size. 

Problem  1.  Care  of  waste  water  pipes.  —  With  regard 
to  the  waste  water  pipes  which  are 
connected  with  the  sewers,  we  are 
chiefly  concerned  with  the  traps, — the 
usual  form  of  which  is  represented  in 
the  diagram  (Figure  128).  Explain 
the  need  of  a  trap.  What  is  apt  to 
happen  to  a  trap  if  considerable  solid 
material  is  allowed  to  enter  the  waste 
pipe  from  the  kitchen  sink?  This 
may  be  largely  prevented  if  a  sink 
strainer  is  used.  Sometimes  the  grease 
from  dishwater  will  collect  in  this 
waste  pipe.  This  may  be  avoided 

by  occasionally  running  through  the  pipe  hot  water  con- 
taining lye.  No  trouble  is  likely  to  occur  in  the  waste  pipe 
of  the  water  closet,  providing  that  pieces  of  newspaper 
and  matches  are  not  thrown  into  it. 

Problem  2.  Sewage  disposal  in  villages  and  isolated 
houses.  —  If  we  live  in  a  city  in  which  there  is  a  well- 

171 


FIGURE  128. — TRAP  OF 
WASTE  WATER  PIPE. 


172 


GENERAL   SCIENCE 


developed  system  of  sewers  there  is  really  no  concern  for  the 
individual  home,  other  than  to  make  sure  that  there  is  a 
proper  connection  with  the  sewer.  In  the  home  or  school 
not  connected  with  a  sewer,  the  septic  tank  system  is  the  most 
satisfactory.  This  consists  essentially  of  two  or  sometimes 
three  concrete  underground  tanks. 


FIGURE  129. — SEPTIC  TANK. 

By  the  overflow  pipe  4  the  waste,  liquified  by  action  of  bacteria,  passes 
into  C,  from  which  it  is  siphoned  into  D,  flowing  out  from  there  by  the 
outlet  pipe. 

In  the  first  tank,  solids  are  acted  upon  by  bacteria  and 
liquified.  By  an  overflow  pipe  this  liquid  passes  into  the 
second  tank,  from  which  it  may  be  removed  through  the 
top ;  or,  in  the  country,  it  may  be  conducted  away  by  a  series 
of  drains  and  permitted  to  escape  into  the  surrounding  soil 
where  it  is  soon  completely  decomposed  by  the  soil  bacteria. 
Any  method  of  disposal  of  waste  from  the  toilet  in  which  the 
material  is  open  to  visits  of  flies,  or  in  which  it  is  permitted 
to  become  mixed  with  the  soil  before  it  has  been  acted  upon 
for  a  long  time  by  bacteria,  is  bad,  as  it  may  mean  exposure 
to  typhoid  fever  and  hookworm  disease. 

Problem  3.  Sewage  disposal  in  cities.  —  The  too  common 
method  has  been  the  easiest ;  that  of  discharging  sewage  into 


TO   UNDERSTAND   THE  DISPOSAL  OF  SEWAGE         173 

streams,  lakes,  or  oceans.  In  th£  cases  of  cities  like  New 
York,  located  on  the  ocean,  this  method  has  not  been  so 
serious  as  in  that  of  cities  on  lakes  and  rivers.  Previous  to 
1900  the  sewage  of  Chicago  was  emptied  into  Lake  Michigan, 
from  which  body  of  water  the  city  also  obtained  its  drinking 
water.  The  average  annual  death  rate  from  typhoid  fever 
for  the  ten  years  preceding  1900  was  66.8  per  100,000.  In 
that  year  the  drainage  canal  was  completed  by  which  the 
Chicago  River,  which  emptied  into  Lake  Michigan,  was 
connected  with  the  Illinois  River,  which  empties  into  the 
Mississippi  River.  So  the  lake  water  which  now  flows 
toward  the  Gulf  of  Mexico  carries  away  with  it  the  sewage 
of  Chicago,  leaving  the  lake  uncontaminated. 

In  the  ten  years  following  the  opening  of  the  canal,  the 
annual  death  rate  from  typhoid  fever  fell  to  22.3  per  100,000. 
It  was  found  that  pathogenic  bacteria  in  the  Chicago  sewage 
had  disappeared  long  before  the  water  had  reached  the 
Mississippi  River.  The  chief  influences  that  bring  about 
such  a  condition  are  sedimentation,  activity  of  other  micro- 
organisms, light,  temperature,  and  lack  of  food  supply. 

Many  cities  use  a  method  somewhat  similar  to  the  septic 
tank  system  on  a  large  scale.  The  ideal  plan  would  be 
such  treatment  of  sewage  that  the  products  could  be  safely 
used  as  a  fertilizer  to  enable  the  land  to  produce  better 
crops.  A  moment's  thought  will  cause  you  to  realize  what 
an  enormous  amount  of  material,  which  should  be  returned 
to  the  soil,  passes  to  the  ocean  every  day  in  the  sewage 
from  New  York  City  alone. 

Each  pupil  should  find  out  the  method  of  sewage  disposal 
practiced  by  his  community  and  determine  the  points  in 
which  the  system  is  a  good  one  and  points  in  which  it  is 
deficient. 


174  GENERAL  SCIENCE 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Make  a  plan  of  the  sewage  system  of  your  home.     Point  out  the 
advantage  of  the  arrangement.     In  what  way  do  you  think  the  arrange- 
ment might  have  been  improved?    Explain. 

2.  Clean  out  the  various  traps  in  the  waste  water  system. 

REPORTS 

1.  The  transmission  and  the  seriousness  of  the  hookworm  diseasec 

2.  Sewage  disposal  of  a  large  city. 

3.  Sewage  disposal  on  a  farm. 


PROJECT  xvn 

WATER  AS  A  MEANS  OF  TRANSPORTATION 

IN  addition  to  the  value  of  water  in  the  air,  as  rainfall ; 
in  furnishing  power,  from  waterfalls ;  for  various  industrial 
purposes;  and  for  drinking  and  household  uses,  it  also 
furnishes  one  of  the  chief  means  of  transportation.  The 
location  of  cities  and  the  development  of  nations  have  been 
determined  by  opportunities  for  utilizing  water  trans- 
portation. The  development  of  New  York  into  one  of  the 
largest  cities  of  the  world  has  been  greatly  influenced  by  the 
fact  that  it  possesses  a  harbor  which  is  almost  unrivaled. 
In  the  same  way,  Boston,  Philadelphia,  and  Baltimore 
on  the  Atlantic  Coast ;  St.  Louis  and  New  Orleans  on  the 
Mississippi;  Chicago,  Buffalo,  Cleveland,  Detroit,  and 
Duluth  on  the  Great  Lakes ;  and  San  Francisco,  Portland, 
and  Seattle  on  the  Pacific  Coast,  owe  much  to  the  advantages 
which  they  offer  to  water  transportation.  Africa  has  few 
harbors,  Europe  has  many.  Explain  how  this  fact  may  have 
led  to  the  more  rapid  development  oPcivilization  in  Europe. 

Since  harbors  to  such  a  great  extent  determine  the  im- 
portance of  a  country,  we  naturally  ask  how  a  good  harbor 
such  as  that  of  New  York  has  been  formed. 

Problem    1.     How   the    New   York   harbor   originated. 

-Examine  the  outline  map  of  the  harbor  (Figure  130). 

Examine  also  the  coast  of  North  America  from  Chesapeake 

Bay  northward  (Figure  131).     Compare  this  coast  line  with 

175 


176 


GENERAL  SCIENCE 


the  western  coast  line  of  South  America  (Figure  132). 
There  is  evidence  that  the  western  coast  line  of  South 
America  is  rising. 


•MAD  OF 
NEW-YOBIK1TY 


A   * 


FIGURE  130.  —  MAP  OF  NEW  YORK  HARBOR. 

Another  fact  to  be  noticed  is  that  the  Hudson  River  is 
very  deep,  permitting    very  large    vessels  to  pass  up    its 


WATER  AS  A  MEANS  OF   TRANSPORTATION 


177 


waters  a  considerable  distance.  Those  of  you  who  are  ac- 
quainted with  the  river  know  that  the  tide  extends  166 
miles  up  the  river  to  Troy  above  Albany. 

How  can  we  explain  the  shape  and  depth  of  the  harbor,  the 
depth  of  the  river,  and  the  fact  that  the  surface  of  the  water 
of  the  river  is  at  sea  level  for  over  one  hundred  and  fifty 
miles     above     its 
mouth  ? 

Since  the  smooth 
coast  line  of  west- 
ern South  America 
is  known  to  be  due 
to  an  elevation  of 
the  land,  we  might 
suspect  that  the 
very  irregular  coast 
line  of  eastern 
North  America  is 
due  to  a  sinking 
of  the  land.  If 
this  is  true  will  that 
account  for  the  con- 
ditions of  the  New 


FIGURE  131. — COAST  OF  EASTERN  UNITED  STATES. 

The  heavy  black  line  marks  the  distance  the 
tide  extends  up  the  rivers. 


York  harbor? 

All      evidence 
seems  to  point  to 

the  fact  that  New  York  harbor  originated  as  did  a  great 
many  good  harbors  by  a  sinking  of  the  coast  (Figure  133). 
This,  of  course,  occurred  many  thousands  of  years  ago  in 
what  we  call  prehistoric  times. 

From  what  we  learn  by  studying  the  earth's  crust  we 
know  that  although  we  may  think  of  the  earth  a§  the  symbol 


178 


GENERAL   SCIENCE 


of  solidity,  portions  of  the  earth's  surface  have  at  times 
been  raised  and  at  other  times  depressed.  The  stratified 
sandstone,  limestone,  and  slaty  rocks  found  over  a  great 
part  of  the  country  are  evidences  of  the  elevation  of  these 

portions  of  the  con- 
tinent, as  these  rocks 
are  formed  only  at  the 
bottom  of  the  ocean 
(Figure  134). 

Problem  2.  Effect 
of  the  forests  of  the 
Adirondacks  upon 
New  York  harbor  and 
the  navigability  of  the 
Hudson  River.  —  In 
order  that  a  harbor 
may  be  of  the  great- 
est value,  a  certain 
amount  of  dredging 
must  be  done  to  keep 
the  channels  free  of 
sand  and  mud.  The 
origin  of  this  material 
will  be  understood  by 
anyone  who  has  no- 
ticed the  appearance 
of  the  water  in  a  small 

stream  after  a  rainstorm.  If  this  small  stream  empties 
into  a  large  body  of  water,  it  will  be  noticed  that  the  mud 
and  sand,  which  is  being  carried,  is  dropped. 

Streams   everywhere   are   wearing   away   the    land   and 
carrying  it  to  the  ocean.    This  is  the  cause  of  much  of  the 


FIGURE  132.  —  OUTLINE  OF  SOUTH  AMERICA. 


WATER  AS  A  MEANS  OF  TRANSPORTATION 


179 


irregularity  of  the  land  surface.  Each  little  stream  forms  a 
ravine  or  valley  of  its  own,  carrying  away  the  particles  of 
earth  and  rock  which  have  been  loosened  by  changes  of 
temperature,  by  the  freezing  of  water  in  crevices,  or  by  the 
action  of  the  oxygen 
or  carbonic  acid  of  the 
air.  The  action  of 
these  agencies  is 
known  as  weathering. 
These  particles,  car- 
ried along  by  the 
swiftly  moving  water, 
help  to  wear  away 
the  bed  of  the  stream ; 
this  is  known  as 
erosion  (Figure  135). 
Thus  we  see  that  the 
land  is  gradually  being 
carried  to  the  ocean, 
where  it  is  dropped  as 
soon  as  the  velocity  of 
the  water  is  checked 
by  coming  in  contact 
with  the  greater  body 
of  water.  Nearly  all 
the  streams  that  form 
the  Hudson  River 
begin  in  the  Adirondack  Mountains,  about  3000  feet  above 
sea  level.  What  must  be  true  of  the  velocity  of  the  water 
of  these  streams?  As  the  rainfall  in  the  Adirondacks  is 
not  evenly  distributed  throughout  the  year,  what  would 
you  expect  to  be  the  condition  of  the  streams  during  the 


FIGURE  133. — OUTLINE  MAP  OF  ENGLAND. 

Note  the  fine  harbors  at  the  mouth  of  the 
rivers.  These  were  produced  by  a  sinking  of 
the  coast  many  thousands  of  years  ago. 


180  GENERAL   SCIENCE 

season  of  great  rainfall  and  at  the  time  of  the  melting  of 
the  snow?  What  would  you  expect  to  be  the  result  when 
this  water  meets  the  sluggish  current  of  the  tidal  portion 
of  the  Hudson,  and  when  the  tidal  current  from  the  river 
meets  the  water  of  the  harbor? 


FIGURE  134.  —  STRATIFIED  ROCKS. 

You  will  be  surprised  to  learn  that  the  streams  are  not 
nearly  so  flooded,  and  that  there  is  not  so  much  sediment 
deposited  as  you  would  imagine.  Our  consideration  of  the 
effect  of  forests  upon  water-supply  areas  gives  us  the  key 
to  the  explanation.  The  Adirondack  Mountains  are  heavily 
forested.  What  effect  does  this  have  upon  the  volume  of 
water  in  its  streams  ?  What  also  will  be  the  effect,  upon  the 
power  of  the  streams  to  accomplish  erosion  and  to  carry 
mud,  sand,  and  rocks?  What  do  you  think  would  be  the 


WATER  AS  A  MEANS  OF  TRANSPORTATION          181 

result  of  cutting  the  forests  from  this  mountainous  region 
as  affecting  the  navigability  of  the  Hudson  River  and  New 
York  harbor? 

In  parts  of  the  country  from  which  the  forests  have  been 
removed,  great  floods  occur  in  the  rainy  periods  of  the  year, 
while  at  other  times  the  navigable  streams  become  too 


FIGURE  135.  —  EROSION  BY  SMALL  STREAM. 

After  heavy  rains  and  after  melting  of  snow  this  stream  becomes  a 

torrent.     The  forests  on  the  mountains  in  the  background  have  been 

burned  away. 

shallow  to  permit  the  passage  of  boats.  Their  navigability 
can  be  maintained  throughout  the  year  only  by  the  expendi- 
ture of  large  amounts  of  money  for  the  purpose  of  dredging 
the  channels  and  of  building  dikes  and  dams. 

These  conditions  are  especially  true  of  the  Ohio  River  and 
its  tributaries.  A  large  part  of  the  drainage  area,  which  was 
at  one  time  densely  wooded,  has  developed  into  a  rich  agri- 
cultural region  necessitating  the  removal  of  most  of  the 
forests.  As  a  result,  during  the  summer  there  is  almost  no 


182 


GENERAL  SCIENCE 


water  except  in  the  larger  streams,  while  in  the  spring  they 
overflow  their  banks,  causing  much  damage  to  property  and 
often  loss  of  lives  (Figure  136). 

Problem  3.  Importance  of  internal  waterways.  —  For  the 
transportation  of  articles  of  commerce  in  which  speed  is 
riot  a  prime  requisite,  internal  waterways  might  well  be 


FIGURE  136. — FLOOD  IN  WABASH  RIVER,  INDIANA. 

This  flood  was  due  to  the  removal  of  forests  from  the  region    of  the 
head  waters  of  the  river. 

used  far  more  than  at  present  because  of  the  smaller  ex- 
pense (Figure  137).  This  would  also  relieve  the  railroads 
so  that  their  facilities  might  be  used  more  completely  in  the 
transportation  of  passengers,  mails,  foodstuffs,  and  articles 
that  demand  quick  delivery  (Figure  138).  Congestion  of 
railroad  traffic  has  been  one  of  the  causes  of  the  high  cost  of 
living.  In  the  great  development  of  railroads  during  the 
past  fifty  years,  the  development  of  transportation  by  water 
has  been  neglected  to  a  large  extent.  An  illustration  of  the 


WATER  AS  A  MEANS  OF  TRANSPORTATION          183 

great  importance  of  river  navigation  is  seen  in  the  carrying 
of  coal  and  iron  from  Pittsburgh  down  the  Ohio  and  Mis- 
sissippi rivers. 

River  traffic  has  been  supplemented  by  the  construction  of 
canals.  Many  of  these  have  fallen  into  disuse  during  the 
period  of  development  of  railroads,  but  recently  steps  have 
been  taken  to  put  some  of  them  into  a  usable  condition. 


FIGURE  137.  —  USE  OF  RIVER  FOR  TRANSPORTATION  OF  LOGS. 

The  first  half  of  the  nineteenth  century  in  the  United 
States  might  almost  have  been  called  the  era  of  canal 
building.  Some  of  the  canals  were  short  ones  around  falls 
in  otherwise  navigable  rivers.  Many  were  of  interest 
because  they  cut  across  watersheds  and  connected  distinct 
drainage  systems,  frequently  at  the  portages  used  by  the 
Indians  and  early  settlers.  If  railroads  had  not  developed 
as  they  did,  we  should  have  had  a  very  complete  system  of 
internal  waterways. 


184  GENERAL   SCIENCE 

The  most  important  of  these  was  the  Erie  Canal,  completed 
in  1825  from  Buffalo  to  Albany,  a  distance  of  352  miles, 
connecting  the  Great  Lakes  with  the  Hudson  River. 
Pennsylvania  and  Maryland  attempted  to  connect  their 
tide- water  rivers  with  the  Ohio  River ;  Virginia  endeavored 
to  connect  Chesapeake  Bay  with  the  Ohio  River;  in  New 
Jersey  the  Morris  Canal  was  built  connecting  New  York 
City  with  the  Delaware  River;  Ohio  and  Indiana  built 
canals  from  the  Great  Lakes  to  tributaries  of  the  Ohio 


FIGURE    138.  —  USE    OF    INTERNAL   WATERWAYS    TO   TRANSPORT  FARM 

PRODUCTS. 

River,  and  in  Illinois  a  canal  was  constructed  connecting 
Lake  Michigan  with  the  Mississippi  system. 

The  "  Soo  "  canal  at  Sault  Ste.  Marie,  between  Lake 
Superior  and  Lake  Huron,  and  the  Welland  ship  canal, 
between  Lake  Erie  and  Lake  Ontario  in  Canadian  territory, 
afford  a  continuous  passage  from  all  parts  of  the  Great 
Lakes  to  the  Atlantic  Ocean  by  way  of  the  St.  Lawrence 
River.  The  route  is  of  especial  interest  to  us  now  because 
in  the  Great  War  many  of  the  large  lake  vessels  were  brought 
to  the  Atlantic  to  be  used  to  carry  troops  and  supplies  to 


WATER  AS  A  MEANS  OF  TRANSPORTATION 


185 


•8 


186  GENERAL  SCIENCE 

Europe.  This  route  has  put  great  areas  of  our  country  into 
direct  water  connection  with  the  markets  of  the  world. 

Problem  4.  How  ocean  transportation  depends  upon 
science.  —  Ocean,  transportation  follows  regular  routes 
which  are  determined  to  some  extent  by  available  harbors, 
prevailing  winds,  ocean  currents,  the  probability  of  the 
presence  of  icebergs,  and  fogs.  In  a  number  of  cases 
routes  have  been  shortened  by  the  construction  of  canals; 
the  two  most  important  ones  are  the  Suez  Canal  through  the 
Isthmus  between  Asia  and  Africa,  connecting  the  Medi- 
terranean Ocean  and  the  Red  Sea,  and  the  Panama  Canal 
through  the  isthmus  between  North  and  South  America, 
connecting  the  Atlantic  and  Pacific  oceans.  Along  our 
eastern  coast,  the  Cape  Cod  Canal  shortens  very  materially 
the  coastwise  route  between  New  York  and  Boston.  The 
Suez  Canal,  opened  in  1869,  has  saved,  in  going  from  the 
North  Atlantic  to  India  and  the  Far  East,  the  long  trip 
around  the  southern  end  of  Africa. 

The  building  of  the  Panama  Canal,  opened  in  1914,  was 
the  greatest  engineering  project  of  the  world.  Its  influence 
upon  the  world's  commerce  is  bound  to  be  very  great. 
It  shortens  the  water  route  from  New  York  to  San  Francisco 
by  almost  8000  miles ;  from  New  York  to  Hawaii  by  about 
6000  miles;  from  New  York  to  Callao  by  about  6000  miles; 
from  New  York  to  Sydney,  Australia,  by  about  4000  miles 
(Figure  140). 

The  building  of  this  canal  was  not  only  an  engineering 
triumph  for  the  United  States,  but  one  equally  great  in  the 
field  of  sanitation.  American  physicians,  by  their  work  in 
the  canal  zone,  not  only  made  possible  the  building  of 
the  canal  but  they  demonstrated  that  tropical  diseases  are 
capable  of  human  control. 


WATER  AS  A  MEANS  OF   TRANSPORTATION 


187 


FIGURE    140.  —  UNITED    STATES  WAR    SHIP   PASSING  THROUGH    PANAMA 

CANAL. 

The  sanitary  work  was  under  the  control  of  Dr.  William 
C.  Gorgas,  who  built  upon  the  work  of  the  United  States 
yellow  fever  commission  in  Cuba,  consisting  of  Drs.  Reed, 
Carroll,  Lazear,  and  Agrimonte,  who  had  proved  at  the  cost 


188 


GENERAL  SCIENCE 


of  the  life  of  Dr.  Lazear  that  the  only  way  that  yellow  fever 
can  be  transmitted  is  by  the  bite  of  a  certain  kind  of  mos- 
quito. Dr.  Gorgas, 
who  had  already 
freed  Havana  and 
Cuba  of  the  yellow 
fever  plague,  was  ap- 
pointed by  President 
Roosevelt  to  con- 
tinue the  work  which 
made  possible  the 
building  of  the  canal. 
The  French  had  been 
defeated  by  the  mos- 
quitoes years  before 
in  their  attempt  to 
build  the  canal  with- 
out even  having 
known  that  these 
insects  were  their 
enemies. 

That  harbors  are 
necessary  for  the  best 
development  of  a 
country  is  realized 
in  comparing  the 
coast  line  of  Africa 
with  its  few  harbors 
to  that  of  Europe 
with  its  many  fine 

ones.     Countries  are  ready  to  go  to  war   to  get  an  outlet 
to  the  sea.     Because  of  the  importance  of  ocean  commerce, 


FIGURE  141.  —  MINOT'S  LEDGE  LIGHTHOUSE. 

This  lighthouse    is   located   on   a  reef  near 

Boston  Harbor. 


WATER  AS  A  MEANS  OF  TRANSPORTATION          189 

nations  have  cooperated  to  encourage  it  in  every  way  possible. 
The  oceans  and  especially  the  waters  near  shores,  where 
most  danger  lies,  have  been  carefully  charted;  lines  of 
magnetic  force  determined  and  charted;  prevailing  winds 
studied;  great  breakwaters  constructed;  harbor  channels 
kept  dredged;  lighthouses,  buoys,  and  foghorns  placed  as 
guides  (Figure  141) ;  life-saving  stations  located  at  inter- 
vals along  the  coasts ;  vessels  and  shipping  offices  furnished 
every  day  with  weather  forecasts  and  special  warnings  on 
the  occasion  of  storms. 

Since  wireless  telegraphy  has  come  into  use,  a  vessel  may 
be  at  all  times  in  touch  with  land  stations  and  other  ships, 
so  that  the  danger  of  serious  results  from  a  breakdown,  fire, 
or  wreck  at  sea  is  very  much  minimized. 

In  addition  to  contributing  largely  to  bringing  about 
the  conditions  just  mentioned,  science  is  being  called  on  for 
help  in  building  larger,  faster,  and  more  seaworthy  ships. 
In  our  own  country  the  demand  of  the  war  for  more  ships 
has  stimulated  shipbuilding  to  such  an  extent  that  the 
United  States  is  destined  to  become  a  leading  ship-owning 
country.  The  ability  of  the  captain  to  sail  his  vessel  and 
bring  it  into  port  depends  upon  his  scientific  training  and  the 
scientific  instruments  which  his  ship  carries.  Without  the 
mariner's  compass,  the  sextant,  the  chronometer,  together 
with  his  charts  and  nautical  almanac,  all  the  results  of 
highly  specialized  science  work,  his  ship  would  be  an  aim- 
less wanderer. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Make  a  collection  of  rocks  from  your  vicinity  accompanied  by  a 
story  of  the  geological  history  of  that  part  of  the  country. 

2.  Construct  a  model  to  illustrate  erosion  and  deposit  of  earth  and 
sand. 


190  GENERAL   SCIENCE 

• 

3.   Construct  a  model  canal  lock  by  which  boats  in  canals  are  passed 
from  one  level  to  another. 

REPORTS 

1.  The  general  geological  history  of  the  North  American  continent. 

2.  A  description  of  the  work  being  done  by  the  government  to  keep 
rivers  and  harbors  navigable. 

3.  The  story  of  the  Erie  Canal. 

4.  History  of  the  building  of  the  Panama  Canal. 

5.  Means  taken  to  prevent  disease  in  the  Panama  Canal  Zone. 

REFERENCES  FOR  PROJECT  XVII 

1.  Panama  and  the  Canal,  Hall  and  Chester.     Newson  and  Co., 
New  York. 

2.  Peeps  at  Many  Lands  (Panama,  the  Canal,  etc.)  Browne.     Mac- 
millan  Company. 

3.  Historic  Inventions,  Holland.     Geo.  W.  Jacobs  Company,  Phila- 
delphia.    (Fulton  and  the  Steamboat.) 

4.  Book  of  the  Ocean,  Ingersoll.     Century  Co. 


UNIT  III 
THE  RELATION  TO  US  OF  SUN,  MOON,  AND  STARS 

PROJECT   XVIII 
TO  UNDERSTAND  THE  CAUSE   OF  TIDES 

ALTHOUGH  so  far  away,  the  sun  and  moon  exert  a 
powerful  influence  upon  everything  that  happens  on  the 
earth.  This  influence  has  been  mentioned  in  considering 
the  source  of  energy  of  food,  coal,  and  wood,  and  the  energy 
of  water  power. 

Then  too,  the  sun,  moon,  and  stars,  although  so  distant, 
have  always  been  of  the  greatest  interest  to  the  inhabitants 
of  the  earth.  The  earliest  speculations  concerning  things 
of  Nature  have  been  concerned  with  these  heavenly  bodies. 
We  know  now  that  much  that  was  fanciful  and  erroneous 
crept  into  their  ideas  of  these  bodies ;  but  we,  just  as  our 
distant  ancestors  were,  are  interested  in  the  wonders  of  the 
heavens.  We,  however,  are  not  satisfied  with  fanciful  imagi- 
nation but  want  to  know  the  truth 

In  our  study  we  shall  begin  with  one  of  the  very  evident 
ways  in  which  the  earth  is  affected  by  the  nearest  of  these 
heavenly  bodies,  the  moon.  A  study  of  the  tides  may 
give  us  some  hints  as  to  the  relationship  between  the  earth 
and  other  heavenly  bodies  and  of  the  relation  of  these  to 
one  another. 

If  you  live  near  the  seashore  or  have  ever  visited  it  you 
know  something  about  tides.  Let  us  first  get  together  our 

191 


192 


GENERAL  SCIENCE 


FIGURE   142.  — HIGH    TIDE    IN    A    HARBOR  IN 
NOVA  SCOTIA. 


observations  con- 
cerning tides.  How 
many  tides  a  day? 
Does  high  tide  oc- 
cur at  the  same 
time  every  day  ? 
If  not,  does  it  oc- 
cur earlier  or  later 
each  day  ?  How 
much  higher  is  the 
water  at  high  tide 
than  at  low  tide 
(Figures  142  and 
143)  ?  Are  there 
any  times  when  the 

tide  is  especially  high  ?    To  find  out  the  cause  of  tides  it  is 

evident  that  we  must  be  able  to  solve  the  following  problems : 
What    causes  the 

rising  of  the  water. 
Why     the     water 

comes    up    twice    a 

day. 

Why  high  tide  is 

a    little    later    each 

day. 

Why,     at     times, 

there   are   especially 

high  tides. 
Problem  1.    What 

causes  the  water  to 

rise.  —  From     the 


FIGURE  143.  —  Low  TIDE  IN  THE  SAME  HARBOR. 


fact   that   the   highest    tides   occur   at   the   time   of   the 


TO   UNDERSTAND   THE  CAUSE  OF   TIDES  193 

full  moon  and  the  new  moon,  what  will  you  suspect  ?  But 
since  the  moon  is  about  240,000  miles  from  the  earth,  at  first 
thought  it  seems  hardly  possible  that  it  can  exert  a  power 
sufficient  to  pull  up  such  an  enormous  amount  of  water. 
This  problem  remained  unsolved  until  Sir  Isaac  Newton, 
in  the  seventeenth  century,  showed  that  the  force  which 
causes  an  object  to  fall  to  the  earth  is  the  same  force  which 
causes  this  tidal  wave  approximately  every  twelve  hours 
and  twenty-five  minutes. 

In  order  to  understand  the  cause  of  tides  it  is  necessary  for 
us  to  consider  this  force.  The  essentials  of  Newton's  dis- 
covery are,  that  every  particle  of  matter  has  an  attraction 
for  every  other  particle  of  matter;  and  that  the  strength 
of  this  attraction  is  directly  proportional  to  the  mass  or 
amount  of  material  and  inversely  proportional  to  the  square 
of  the  distance  between  their  centers.  This  means  that  if 
the  moon  were  twice  as  large,  it  would  pull  upon  the  earth 
with  twice  the  force  it  does  now  and  that  if  it  were  twice 
as  far  from  the  earth  as  now  it  would  pull  upon  the  earth 
with  a  force  only  one  fourth  as  great  as  at  present. 

In  accordance  with  this  law  of  gravitation,  there  is  a  pull 
between  the  center  of  the  earth  and  every  object  we  know. 
The  measure  of  this  pull  constitutes  the  weight  of  a  body. 
The  reason  that  the  earth  does  not  seem  to  be  pulled  toward 
the  ball  that  is  dropping  may  be  understood  from  the  fol- 
lowing experiment. 

Experiment.  —  Connect  two  marbles,  A  and  B,  of  equal  size,  by  a 
rubber  band.  Draw  the  marbles  apart  and  allow  the  elasticity  of  the 
band  to  pull  them  together.  Compare  the  amount  of  movement  of 
each  marble.  Now  connect  a  very  small  marble  with  a  very  large  one 
by  a  rubber  band.  As  before,  compare  the  amount  of  movement  of 
each  when  they  are  pulled  together  by  the  elastic.  If  there  is  ten 


194  GENERAL   SCIENCE 

times  as  much  material  in  the  large  marble  as  in  the  small  one,  the 
large  marble  will  move  one  tenth  as  far  as  the  small  one.  Explain, 
then,  why  the  ball  falls  to  the  earth,  and  why  the  earth  does  not  seem 
to  rise  to  the  ball. 

This  force  acts  in  solid  bodies,  through  the  center  of  mass 
of  the  body.  It  is  because  of  this  that  a  mason's  plumb 
line  points  to  the  middle  of  the  earth  (Figure 
144).  In  objects  on  the  surface  of  the  earth,  this 
center  of  mass  or  center  of  gravity,  as  it  is  called, 
is  the  point  of  a  body  at  which  its  weight  may 
be  counteracted  by  a  single  upward,  vertical  force. 
The  location  of  the  center  of  gravity  is  easily 
found.  Suppose  the  center  of  gravity  of  a  piece 
of  cardboard  is  to  be  found.  Suspend  the  card- 
board by  a  thread.  Draw  a  line  on  it  continuous 
with  the  line  of  the  supporting  thread.  Now  sus- 
pend the  cardboard  in  the  same  way  from  another 
point  of  attachment.  The  point  of  intersection 
of  the  two  lines  will  be  the  location  of  the  center 
of  gravity.  Explain. 

The  fact  that  the  center  of  gravity  of  a  body 
tends  to  get  as  near  the  center  of  the  earth  as  pos- 
sible is  illustrated  by  the  tipping  over  of  bodies. 
FIGURE  144.  Why  does  a  flat  stone  on  the  ground  show  no 
PLUMB  LINE,  tendency  to  tip,  while  the  same  stone  standing 
on  its  edge  tips  over  very  easily?  A  body  is  said  to  be 
in  stable  equilibrium  when  it  cannot  be  tipped  without 
raising  its  center  of  gravity ;  a  body  is  in  unstable  equilibrium 
when  it  cannot  be  tipped  without  lowering  its  center  of 
gravity  (Figure  145). 

Let  us  now  go  back  to  the  tides  and  endeavor  to  under- 
stand how  this  force  of  gravitation  causes  them.     The  moon 


TO   UNDERSTAND   THE  CAUSE  OF   TIDES 


195 


attracts  the  solid  earth  as  if  the  entire  mass  of  the  earth 

were  concentrated  at  its  center.     The  water  of  the  ocean, 

however,    is    4000    miles 

from    the   center   of   the 

earth.     What,    therefore, 

is    the    relative    pull    of 

the  moon  upon  the  solid 

earth,  and  upon  the  ocean 

on   the   side   nearest   the 

moon?       (Figure      146). 

rjM.-     •     .a.  e  xil  FIGURE  145. 

This  is  the  cause  of  the       ^  stable  equihbrium.    B>  unstable 

tide    On   the    side    of    the        equilibrium.    C,  neutral  equilibrium. 

earth  nearest  the  moon. 

Problem  2.  Why  there  are  two  high  tides  a  day.  —  You 
already  know  from  your  study  of  geography  that  the  earth 
rotates  once  in  twenty-four  hours.  Therefore,  how  many 

Low  WATER. 


THE  MOON. 


Low  WATBTR. 

FIGURE  146.  —  RELATION  OF  MOON  TO  THE  TIDES. 

times  a  day  is  the  moon  directly  opposite  any  part  of  the 
earth?  It  can  be  easily  understood,  then,  how  a  wave  of 
water  will  travel  around  the  earth.  In  what  direction  will 
it  travel?  Explain.  (Note:  Does  the  moon  rise  in  the 
east  or  the  west?)  According  to  this,  how  many  tides  a 
day  will  there  be?  But,  in  reality,  how  many  are  there 
(Figure  146)  ? 


196  GENERAL   SCIENCE 

From  the  fact  that  high  tides  are  about  twelve  hours 
apart  when  there  is  high  tide  on  any  part  of  the  earth,  at 
what  other  part  of  the  earth  is  the  other  high  tide?  Our 
problem  then  is,  how  is  this  second  high  tide,  on  the  side  of 
the  earth  away  from  the  moon,  caused. 

Recall  the  way  in  which  gravitation  acts  upon  the  solid 
earth  and  upon  the  water  of  the  ocean.  How  much  farther 
away  from  the  moon  is  the  water  on  the  opposite  side  of  the 
earth  than  the  center  of  gravity  of  the  solid  earth?  Upon 
which,  therefore,  will  the  pull  be  greater?  It  can  be  under- 
stood now  how  there  is  a  tendency  for  the  solid  earth  to  be 
pulled  away  from  the  water  and  as  a  result  the  water  will 
flow  in,  causing  an  elevation  of  the  water,  thus  producing  a 
tidal  wave  on  the  side  of  the  earth  away  from  the  moon. 
In  what  direction  will  this  tidal  wave  travel  and  at  what 
rate  compared  with  the  tidal  wave  directly  under  the  moon  ? 
There  is  also  another  force  which  helps  produce  this  tidal 
wave  on  the  side  of  the  earth  away  from  the  moon,  which 
can  be  understood  a  little  later. 

Problem  3.  Why  high  tide  is  a  little  later  every  day.  — 
From  our  discussion,  what  would  you  conclude  should  be 
the  time  between  two  high  tides  ?  If,  then,  high  tide  occurs 
at  12  o'clock  on  one  day,  at  what  time  should  there  be  high 
tide  on  the  following  day?  Is  this  actually  what  occurs? 
Some  of  you  have  gone  to  the  ocean  bathing  beaches.  On 
your  visits  there  did  you  find  that  high  tide  always  occurred 
at  the  same  time  of  day  ? 

Observation  will  show  you  that  high  tide  is  about  fifty 
minutes  later  every  day.  Our  problem  then  is  to  under- 
stand the  reason  for  this  seeming  discrepancy. 

In  our  discussion  of  the  cause  of  tides  we  considered  that 
.  the  earth  rotated  once  in  twenty-four  hours.  If  the  moon 


TO    UNDERSTAND   THE   CAUSE  OF   TIDES  197 

kept  in  the  same  relative  position  with  reference  to  the 
earth,  how  often  would  a  certain  point  on  the  earth's  sur- 
face be  directly  opposite  the  moon?  Since,  however,  it 
takes  twenty-four  hours  and  fifty  minutes  for  any  spot 
which  is  directly  opposite  the  moon  to  be  again  opposite 
the  moon,  what  will  be  your  conclusion  as  to  the  movement 
of  the  moon  ?  Can  you  determine  whether  the  moon  moves 
around  the  earth  in  the  same  direction  as  the  earth  rotates 
or  in  the  opposite  direction  ? 

Astronomers,  scientists  who  study  the  movements  of  the 
heavenly  bodies,  have  shown  that  the  conclusion  we  have 
reached  that  the  moon  revolves  around  the  earth  in  the 
same  direction  in  which  the  earth  rotates  is  true.  They 
tell  us  that  the  moon  revolves  completely  around  the  earth 
in  twenty-eight  days.  We  can  now  consider  the  problem 
which  arose  in  discussing  gravitation. 

Problem  4.  Why  the  moon  does  not  fall  to  the  earth.  — 
You  have  probably  wondered  why,  if  the  earth  and  moon 
are  pulling  each  other,  they  do  not  come  together  just  as 
we  found  that  the  rubber  band  pulled  the  two  marbles  to- 
gether. In  order  to  understand  this,  we  must  know  that  the 
moon  revolves  around  the  earth  once  in  twenty-eight  days. 
This  is  the  explanation  of  the  fact  that  the  moon  rises  about 
one  hour  later  every  night.  If  the  moon  occupied  con- 
tinuously the  same  relative  position  to  the  earth,  it  would 
rise  at  the  same  time  every  night.  What  would  be  the  time 
between  high  tides  ?  What  is  the  time  between  high  or  low 
tides? 

The  way  in  which  the  revolution  of  the  moon  around  the 
earth  prevents  it  from  falling  to  the  earth  is  illustrated  by 
many  very  common  happenings.  What  happens  when  you 
swing  in  a  vertical  circle  a  pail  containing  water?  What 


198  GENERAL  SCIENCE 

happens  to  the  water  on  a  grindstone,  when  it  is  turned 
rapidly?  What  happens  to  an  automobile  if  it  attempts 
to  turn  a  corner  too  rapidly?  What  is  the  advantage  of 
having  a  circular  running  track  "  banked  "  ?  Wet  clothes 
are  dried  by  putting  them  into  a  large,  perforated,  metal 
cylinder  and  rotating  the  cylinder  rapidly.  If  you  are 
familiar  with  milk  separators,  explain  how  the  milk  is 
separated  from  the  cream  (Figure  147). 

All  of  these  observations,  showing  that  rotating  bodies 
tend  to  fly  away  from  the  center  around  which  the  body  is 


.'  -  .- ,:          FIGURE  147. 

Why  do  the  mercury  and  water  not  remain  at  the  bottom 
of  the  glass  globe? 

turning,  are  illustrations  of  the  fact,  that  bodies  in  motion 
tend  to  remain  in  motion  in  a  straight  line.  They  are 
illustrations  of  a  law  stated  by  Sir  Isaac  Newton,  known  as 
Newton 's  first  law  of  motion:  ''Every  body  continues  in  its 
state  of  rest  or  of  uniform  motion  in  a  straight  line,  except  in 
so  far  as  it  is  compelled  by  force  to  change  that  state."  Give 
other  illustrations  of  the  law. 

For  every  body  turning  around  a  center  there  must  be  two 


TO   UNDERSTAND   THE  CAUSE  OF  TIDES  199 

forces ;  one  drawing  it  toward  the  center,  called  the  centrip- 
etal force  (center-seeking  force) ;  and  one  drawing  it  away 
from  the  center,  called  the  centrifugal  force.  The  moon 
revolves  around  the  earth  once  in  every  twenty-eight  days. 
As  the  moon  is  240,000  miles  from  the  earth,  you  can  easily 
calculate  its  velocity.  Because  of  this  motion  what  does  the 
moon  tend  to  do?  What  prevents  it?  In  your  own  lan- 
guage explain  why  the  moon  is  not  drawn  to  the  earth  or 
does  not  fly  off  into  space. 

You  will  recall  that  in  discussing  the  cause  of  the  tide 
on  the  side  of  the  earth  away  from  the  moon  reference  was 
made  to  another  force  in  addition  to- the  difference  of  the 
pull  of  gravitation  upon  the  solid  earth  and  the  liquid  ocean. 
This  force  we  can  now  understand.  The  moon  and  earth 
are  held  together  by  the  force  of  gravitation  very  much  as  a 
large  man  and  a  small  boy  might  hold  themselves  together 
by  locking  their  hands  together. 

If,  while  holding  hands  in  this  way,  the  man  should 
swing  the  boy  around,  not  only  would  the  boy  tend  to 
swing  in  as  large  a  circle  as  possible,  but  the  coat  tails  of  the 
man  also  would  tend  to  fly  out  because  of  the  centrifugal 
force.  In  the  same  way  the  water  on  the  side  of  the  earth 
away  from  the  moon  tends  to  heap  up  because  of  this  centrif- 
ugal force. 

There  remains  yet  one  problem  concerning  tides  which 
we  decided  needed  solution :  Why,  at  times,  there  are  es- 
pecially high  tides. 

Problem  5.  Why,  at  times,  there  are  especially  high 
tides.  —  Usually  about  twice  a  month  the  tides  are  es- 
pecially high.  During  the  winter  of  1919-1920  such  a  tide 
accompanied  by  a  wind  from  the  ocean  flooded  Coney 
Island  and  Rockaway  Beach  near  New  York,  wrecking 


200 


GENERAL  SCIENCE 


many  buildings.     At  the  same  time  a  large  part  of  the 
water  front  of  New  York  City  was  covered  with  water. 


FULL  MOON. 


€> 


FIGURE  148. — THE  Two  POSITIONS  OF  THE  MOON  WHEN  HIGH  TIDE 
Is  HIGHER  THAN  USUAL. 

This  occurred  at  the  time  of  the  full  moon.    At  every  full 
moon  and  new  moon  the  tide'  is  especially  high.     On  the 
—  other     hand,  .  when 

*•(        )  FIRST  QUARTER  the  moon  is  at  first 


MOON. 


Y 

; 

NEAP-TIDE. 


and  third  quarters, 
the  high  tides  are 
especially  low. 


The  accompanying 
diagrams  (Figures 
148  and  149)  show 
the  relative  positions 
of  the  earth,  moon, 
and  sun  at  these 
times.  From  exam- 
ination of  these 
diagrams  explain  the 
cause  of  the  espe- 
cially high  tides  at 
certain  times. 

Evidently  the 
theory  that  the  tides  are  caused  by  the  force  of  gravitation, 
studied  by  Sir  Isaac  Newton,  can  be  accepted,  as  it 
offers  a  satisfactory  explanation  of  the  cause  of  tides  and 


NEAP-TIDB. 


MOON.f  J  THIRD  QUARTER.      '"• 

FIGURE  149. — THE  Two  POSITIONS  OF  THE 
MOON  WHEN  HIGH  TIDE  Is  NOT  AS  HIGH  AS 
USUAL. 


TO    UNDERSTAND   THE  CAUSE  OF   TIDES 


201 


is  in  harmony  with  all  the  facts  that  we  have  observed 
concerning  them. 

In  mid-ocean  the  tide  cannot  be  observed,  but  it  is  very 
noticeable  when  it  strikes  against  the  land.  Sometimes  be- 
cause of  the  charac- 
ter of  the  coast  line 
the  tides  rise  to  a 
great  height,  as  in 
the  Bay  of  Fundy, 
Nova  Scotia,  where 
they  are  more  than 
sixty  feet  high.  Some 
shallow  harbors  can 
be  entered  or  left 
only  at  high  tide. 

Do  tides  possess 
energy?  Can  you 
suggest  a  way  by 
which  this  energy 
might  be  utilized? 

The  information 
which  we  have 
learned  concerning 
the  movement  of 
the  moon  around 
the  earth  may  help 
us  to  solve  another 
problem. 

Problem  6.  Why  sometimes  only  a  portion  of  the  moon 
is  visible  to  us.  —  At  first  sight  this  seems  a  difficult  prob- 
lem, but  answering  the  following  questions  may  help  us. 

1.   Is  the  moon  cold,  or  hot  like  the  sun? 


FIGURE  150.  —  PHASES  OF  THE  MOON. 

The  outside  circle  of  positions  of  the  moon 
shows  the  part  lighted  by  the  sun.  The  inner 
positions  indicate  how  the  moon  appears  to 
us  in  its  different  positions. 


202 


GENERAL   SCIENCE 


2.  What  is  the  source  of  the  light  which  comes  to  us  from 
the  moon? 

3.  What  motion  has  the  moon  in  relation  to  the  earth? 

4.  How  long  does  it  take  the  moon  to  go  around  the 
earth? 

5.  About  how  often  do  we  have  a  full  moon? 

An  examination  of  the 
following  diagram,  in  con- 
nection with  the  answers 
to  the  questions  above, 
will  make  clear  to  you  why, 
at  times,  the  moon  appears 
like  a  ball,  while  at  other 
times  it  appears  as  a  cres- 
cent. Even  when  the  moon 
appears  only  as  a  crescent 
we  can  sometimes  dimly 
see  the  remaining  portion 
of  its  surface.  This  is  be- 
cause of  reflection  of  light  from  the  surface  of  the  earth. 

The  following  lines  will  enable  you  to  know  whether  the 
crescent  you  see  in  the  sky  is  an  old  or  new  moon : 
"  Oh,  Lady  Moon,  your  horns  point  toward  the  east.     Shine ; 

be  increased ! 

Oh,  Lady  Moon,  your  horns  point  toward  the  west.     Wane ; 
be  at  rest ! " 

Occasionally  an  eclipse  of  the  sun  occurs.  If  we  look  at 
the  sun  at  such  a  time  through  a  piece  of  smoked  glass,  it 
will  be  noticed  that  a  rounded  black  notch  or  patch  appears 
on  the  edge  of  the  sun.  This  black  patch  travels  across  the 
surface  of  the  sun.  If  the  eclipse  is  a  total  one,  it  obscures 
for  a  short  time  the  entire  face  of  the  sun  (Figure  151) ;  if, 


FIGURE  151.  —  A  TOTAL   ECLIPSE  OF 
THE  SUN. 


TO   UNDERSTAND   THE  CAUSE  OF   TIDES 


203 


as  is  usual,  the  eclipse  is  only  partial,  only  a  segment  of  it  is 
obscured. 

Considering  the  relative  location  of  the  bodies  of  the 
solar  system,  what  do  you  believe  causes  an  eclipse  of  the 
sun?  There  may  also  be  an  eclipse  of  the  moon.  Sug- 
gest how  this  may  occur.  Draw  diagrams  showing  the 
relation  of  the  moon, 
earth,  and  sun  in  both 
kinds  of  eclipse.  The 
accuracy  with  which  the 
time  of  an  eclipse  may  be 
foretold  years  in  advance 
of  the  event  is  an  indi- 
cation of  how  thoroughly 
the  laws  of  motions  of 
the  members  of  the  solar 
system  are  understood. 

Solar  system.  —  The 
same  two  forces  which 
hold  the  moon  in  its  path  keep  the  earth  and  other  planets 
in  their  orbits  or  paths  around  the  sun.  In  the  order  of 
their  distance  from  the  sun  the  planets  are  Mercury, 
Venus,  Earth,  Mars,  Jupiter,  Saturn,  Uranus,  and  Neptune 
(Figure  152)  To  us,  Venus  is  the  most  conspicuous  of 
these  planets.  Next  to  the  sun  and  moon  it  is  the  brightest 
object  in  the  sky.  At  times  it  is  the  evening  star,  and  at 
other  times  the  morning  star. 

Mars,  which  sometimes  appears  as  a  reddish  star  in  the 
sky,  has  been  a  favorite  object  for  study  with  the  telescope 
because  of  its  nearness  and  especially  because  in  many  re- 
spects it  resembles  the  earth,  leading  observers  to  think  that 
possibly  life  similar  to  that  on  the  earth  may  exist  there. 


FIGURE   152. 


DIAGRAM  OF  OUR  SOLAR 
SYSTEM. 


204  GENERAL  SCIENCE 

The  thinness  of  the  atmosphere  and  the  small  amount  of 
water  present  on  Mars  render  this  belief  rather  improbable. 
The  sun  with  the  planets  revolving  around  it  is  called  the 
solar  system.  The  sun  is  a  light-giving  body;  the  planets 
and  their  moons  only  reflect  the  light  of  the  sun. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Make  a  model  to  scale  showing  the  relative  size  of  the  moon 
and  the  earth,  and  the  distance  of  the  moon  from  the  earth. 

2.  Make  a  diagram  showing  the  location  of  the  moon  in  the  sky  at 
a  certain  hour  on  six  successive  nights.     Show  also  the  appearance  of 
the  moon  each  night.     Explain  your  observations. 

3.  Work  out  a  plan  of  the  solar  system,  representing  to  scale  the 
relative  distances  and  sizes  of  the  sun  and  the  planets. 

4.  Make  a  model  of  sun,  earth,  and  moon  to  show  the  cause  of 
eclipses,  phases  of  the  moon,  and  seasons. 

REPORTS 

1.  Use  of  the  energy  of  tides. 

2.  How  the  sun,  moon,  and  planets  have  come  into  existence. 

3.  Discussion  of  the  probability  of  life  similar  to  that  on  this  earth 
existing  on  other  planets. 

REFERENCES  FOR  PROJECT  XVIII 

1.  The  Moon,  G.  P.  Serviss.    D.  Appleton  &  Co. 

2.  The  Ways  of  the  Planets,  M.  E.  Marten.     Harper  &  Bros. 

3.  Giant  Sun  and  His  Family,  Proctor.    Silver,  Burdett  &  Co. 


PROJECT   XIX 
HOW  TO  KNOW  SOME  OF  THE  FIXED   STARS 

THE  thousands  of  stars  which  we  see  in  the  heavens  are 
light-giving  bodies,  and  correspond  to  our  sun.  Many  or 
all  of  them  may  be  the  centers  of  solar  systems.  These 
stars  have  a  fixed  position  with  reference  to  one  another 
and  are  accordingly  called  fixed  stars.  From  the  earliest 
times  the  stars  have  been  grouped  and  named  according  to 
objects  to  which  they  seemed  to  bear  a  fanciful  resemblance. 
The  ability  to  recognize  a  few  of  the  more  easily  located 
groups  or  "  constellations  "  adds  much  to  our  enjoyment  of  a 
starry  night 

Problem  1.  How  to  recognize  the  constellations  around 
the  north  pole.  —  The  easiest  way  to  begin  the  study  of  the 
constellations  is  to  locate  the  Great  Dipper,  which  is  known 
by  almost  everyone  (Figure  153).  While  the  Great  Dipper 
is  always  in  the  northern  part  of  the  sky,  it  does  not  appear 
at  all  times  in  the  same  position,  as  the  stars  seem  to  re- 
volve around  a  fixed  point  in  the  sky.  The  bright  star 
located  at  this  point  is  called  the  Pole  or  North  Star. 
Explain  why  these  terms  are  appropriate. 

The  Pole  Star  can  be  located  by  looking  along  a  line  which 
is  a  continuation  of  the  line  connecting  the  two  stars  form- 
ing the  front  of  the  bowl  of  the  Great  Dipper.  These  stars 
are  called  the  Pointers.  The  Pole  Star  is  along  the  line  a  dis- 
tance of  about  five  times  the  distance  between  the  Pointers, 
or  about  twenty-five  degrees,  since  the  distance  between  the 

205 


206 


GENERAL   SCIENCE 


Pointers  is  approximately  five  degrees.  It  will  be  well  to 
keep  these  figures  in  mind,  as  they  will  serve  as  standards 
for  measuring  distances  between  stars. 

The  Pole  Star  is  part  of  a  constellation  called  the  Little 
Dipper.  It  also  has  seven  stars,  the  number  that  you  have 

seen  in  the  Great 
Dipper.  The  out- 
line of  the  Little 
Dipper,  however, 
is  not  so  distinct 
as  that  of  its  big 
namesake.  The 
Pole  Star  is  at 
the  end  of  the 
handle  of  the 
Little  Dipper. 
The  bowl  is  com- 
posed of  a  clus- 
ter of  four  stars, 
the  two  of  the 
outer  rim  being 
the  brightest,  lo- 
cated about  fifteen  degrees  from  the  Pole  Star  and  facing 
the  open  bowl  of  the  Great  Dipper.  If  you  have  found 
the  stars  of  the  bowl,  the  other  two  stars  of  the  handle 
may  be  easily  located  between  the  bowl  and  the  Pole  Star. 
It  will  be  noticed  that  the  end  of  the  handle  of  the  Little 
Dipper  is  bent  in  a  different  direction  from  that  of .  the 
handle  of  the  Great  Dipper. 

The  ancients  imagined  the  stars  of  the  Great  Dipper  to 
represent  the  form  of  a  great  bear,  and  this  constellation 
was  accordingly  called  Ursa  Major  or  the  Great  Bear. 


FIGURE    153.  —  CONSTELLATIONS   AROUND    THE 
NORTH  STAR. 


HOW   TO  KNOW  SOME  OF   THE  FIXED   STARS         207 

Likewise  the  Little  Dipper  was  called  Ursa  Minor  or  the 
Little  Bear.  The  ability  to  see  a  small  star  in  the  handle 
of  the  Great  Dipper  is  frequently  used  as  a  test  for  good 
sight.  Look  at  the  second  star  counting  from  the  end  of 
the  handle.  This  is  called  Mizar.  Directly  above  it  at 
a  distance  of  about  one  degree  is  the  faint  star  Alcor.  The 
Arabs  call  these  two  stars  "  the  horse  and  the  rider. " 

The  constellation  Cassiopeia's  Chan*  is  located  about  the 
same  distance  from  the  Pole  Star  as  the  Great  Dipper,  but  on 
the  opposite  side.  It  is  very  easily  recognized  because  its 
five  bright  stars  form  a  W-shaped  figure. 

Auriga,  or  the  Charioteer,  contains  one  of  the  brightest 
stars,  Capella,  in  the  northern  part  of  the  heavens.  Ca- 
pella  is  about  forty-five  degrees  from  the  Pole  Star ;  that  is, 
almost  twice  as  far  away  as  the  Great  Dipper  or  Cassiopeia's 
Chair,  and  on  a  line  drawn  at  right  angles  to  a  line  connect- 
ing the  Pointers  with  the  Pole  Star.  Another  way  to  find 
Capella  is  to  follow  a  line  drawn  from  the  star  at  the  bottom 
of  the  Great  Dipper  that  is  nearest  to  the  handle,  and  pass- 
ing halfway  between  the  Pointers.  At  a  distance  of  about 
fifty  degrees  along  this  line,  Capella  will  be  seen  as  a  very 
bright  star.  Capella  with  the  four  other  brightest  stars 
of  the  constellation  form  a  pentagon  or  five-sided  figure. 

The  brightest  stars  of  the  constellation  Perseus  lie  in 
an  arc  extending  from  Capella  to  Cassiopeia's  Chair.  You 
will  be  able  to  see  along  this  arc  six  or  seven  stars  that  be- 
long to  the  constellation. 

Other  rather  conspicuous  constellations  which  may  be 
seen  within  a  radius  of  about  forty  or  forty-five  degrees 
of  the  Pole  Star  are  the  Dragon,  and  Cepheus. 

Problem  2.  How  to  recognize  the  constellations  seen 
only  in  winter.  —  Stars  farther  away  from  the  pole  can  be 


208 


GENERAL  SCIENCE 


seen  only  at  certain  times  of  the  year.  The  best-known 
of  the  winter  constellations,  located  on  a  line  passing  almost 
directly  overhead  from  east  to  west,  is  Orion,  the  Hunter. 
It  is  easily  recognized  by  the  three  stars  forming  the  belt. 


FACE  SOUTH  ANL 
HOLD  THE  MAP  OVER 
YOUR  HEAD-THE 


NORTH;  AND  YOU  WILL  SEE 

BfAWMBF 

IN  THE  HEAVENS 


THE  ARROW  THROUGH 
THE  TWO  STARS  IN  THE 
BOWL  OF  THE  BIG  DIPPED 
INTS  TO  THE  NORTH  STAR- 
THE  STAR  AT  THE  END  OF  THE 
HANDLE  OF  THE,  LITTLE  DIPPER. 


FIGURE  154. — EVENING  SKY  MAP  FOR  JANUARY,  1921. 

Except  for  the  planets  the  sky  is  always  the  same  as  above  in  Jan- 
uary. Note  the  planets  on  the  ecliptic  :  Mars  the  farthest  to  the  west, 
with  Venus  near  it,  and  Neptune  in  the  east. 

Several  small  stars,  extending  at  almost  right  angles,  con- 
stitute the  sword  hanging  from  his  belt  (Figure  154). 
A  very  bright,  reddish  star,  Betelgeuse,1  marks  the  right 

1  The  diameter  of  Betelgeuse  was  recently  measured  for  the  first 
time  with  an  instrument  devised  by  Professor  Albert  A.  Michelson  of 
the  University  of  Chicago.  The  star  was  found  to  be  about  27,000,000 
times  larger  than  our  sun. 


HOW  TO  KNOW  SOME  OF  THE  FIXED  STARS        209 

shoulder,  while  another  bright  star,  Rigel,  white  instead  of 
reddish,  is  located  in  the  left  foot  of  the  great  hunter.  After 
you  have  located  these  stars,  you  will  be  able  to  make  out 
the  stars  which  represent  the  lion's  skin  which  hangs  from 
his  left  arm,  and  the  stars  of  the  right  arm  and  of  the  club. 

Facing  Orion,  and  between  him  and  the  Pole  Star,  is  the 
constellation  Taurus,  or  the  Bull.  The  face  of  the  Bull 
is  represented  by  several,  stars  arranged  in  the  form  of  a  V. 
The  bright  red  star,  Aldebaran,  at  the  top  of  the  left  branch 
of  the  V  is  the  eye  of  the  Bull. 

The  constellation  called  the  Pleiades,  or  Seven  Sisters, 
is  in  the  shoulder  of  the  Bull.  The  stars  of  this  constella- 
tion, six  of  which  can  easily  be  seen,  are  very  close  together 
and  arranged  in  the  form  of  a  very  small  dipper. 

Farther  south  in  the  winter  sky  may  be  seen  the  constella- 
tions whose  brightest  stars,  Sirius  and  Procyon,  are  called 
the  hunting  dogs  of  Orion.  Sirius,  the  brightest  of  the 
fixed  stars,  seems  to  follow  at  the  heels  of  Orion  and  may 
easily  be  located  by  following  a  line  passing  from  the  eye  of 
the  Bull,  Aldebaran,  through  the  belt  of  Orion  and  beyond 
about  twenty  degrees.  Procyon,  Sirius,  and  Betelgeuse 
make  a  triangle,  each  side  of  which  is  about  twenty  de- 
grees. 

If  you  have  located  the  constellations  which  have  been 
named  in  the  preceding  pages,  you  will  be  able  with  the 
help  of  the  many  excellent  books  about  the  stars,  to  locate 
other  constellations,  especially  the  most  conspicuous  ones 
of  the  spring  and  summer  skies;  the  Lion  and  the  Twins 
seen  in  the  spring,  and  the  Virgin,  the  Herdsman,  the  North- 
ern Crown,  and  the  Scorpion  in  the  summer. 


210  GENERAL  SCIENCE 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Identify  at  least  eight  constellations. 

2.  Work  out  the  method  of  reading  star  maps.    Collect  and  mount 
star  maps  for  every  month. 

REPORT 
Origin  of  the  names  of  some  of  the  constellations. 

REFERENCES  FOR  PROJECT  XIX 

1.  A  Beginner's  Star  Book,  Kelvin  McKready.     G.  P.  Putnam's 
Sons. 

2.  The  Barritt-Serviss  Star  and  Planet  Finder,  Leon  Barritt,  367 
Fulton  St.,  Brooklyn,  N.  Y. 

4.  Astronomy  with  the  Naked  Eye,   G.  P.    Serviss.       Appleton 
&Co. 

5.  Star  Lore  of  All  Ages,  W.  T.  Olcutt.     G.  P.  Putnam. 

6.  Earth  and  Sky  Every  Child  Should  Know,  J.  E.  Rogers.     Double- 
day,  Page  &  Co. 

7.  The  Children's  Book  of  Stars,  G.  A.  Milton.    Adam  and  Chas. 
Black,  London. 

8.  The  Friendly  Stars,  M.  E.  Marten.     Harper  &  Bros. 

9.  The  Stars  and  Their  Stories,  Griffith.     Henry  Holt  &  Co. 


PROJECT   XX 
TIME   AND    SEASONS 

SINCE  light  and  heat  come  from  the  sun,  the  difference 
between  winter  and  summer  must  be  in  some  way  associated 
with  some  difference  in  relation  between  the  sun  and  the 
earth.  Likewise  our  calculation  of  time  must  be  based  on 
the  relation  between  the  earth  and  the  sun.  Every  morn- 
ing we  see  the  sun  rise  in  the  east  and  at  the  end  of  the  day 
set  again  in  the  west. 

Problem  1.  Why  we  have  winter  and  summer.  —  There 
are  several  facts  with  which  we  are  familiar  that  will  help  us 
to  understand  the  cause  of  the  seasons.  What  is  the  com- 
parative length  of  day  and  night  during  winter  and  summer? 
What  is  the  relative  height  of  the  sun  above  the  horizon 
at  midday  in  winter  and  in  summer?  Evidently  the  sun 
shines  more  directly  upon  our  part  of  the  earth  in  summer 
than  in  winter. 

We  have  already  learned  that  the  earth  rotates  (turns) 
upon  its  own  axis,  and  revolves  around  the  sun.  If  the 
axis  of  the  earth  is  at  right  angles  to  an  imaginary  line 
running  from  the  earth  to  the  sun,  what  part  of  the  earth 
would  always  receive  the  most  direct  rays  of  the  sun?  But 
since  during  the  summer  the  portion  of  the  earth  north  of  the 
equator  receives  the  most  direct  rays  of  the  sun,  and  during 
the  winter  the  same  region  receives  fewer  direct  rays  of  the 
sun,  what  is  your  conclusion  in  regard  to  the  direction  of 
the  earth's  axis?  (Figure  155.) 

211 


212 


GENERAL  SCIENCE 


Since  on  our  longest  day  in  summer  the  direct  rays  of 
the  sun  strike  a  point  23^  degrees  north  of  the  equator 
and  on  the  shortest  day  of  our  winter  strike  a  point  23J  de- 
grees south  of  the  equator,  we  know  that  the  axis  of  the 

* 


MAACH  ruumtw 


FIGURE  155.  —  HEAT  FROM  SUN,  SUMMER  AND  WINTER. 

earth  is  inclined  23^  degrees  to  the  imaginary  line  running 
from  the  earth  to  the  sun. 

A  careful  study  of  Figure  156  will  make  clear  how  the 
revolution  of  the  earth  and  the  inclination  of  its  axis  cause 
the  seasons. 

1.  At    what    times    in 
the  year  are  the  days  and 
nights    equal   in  length? 
These  times  are  called  the 
vernal  or  spring  equinox, 
and  the  autumnal  or  fall 
equinox. 

2.  On   June  22,   1919, 
at  New  York   City,  the 
sun  rose  at  4 : 28  A.M.  and 

set  at  7 : 35  P.M.  What  was  the  length  of  the  period  of 
daylight?  What  was  the  length  of  the  daylight  period 
within  the  arctic  circle  (23^  degrees  from  the  north  pole) 
on  this  date  ? 

3.   In  your  own  language  discuss  the  changes  in  the  length 


SPTtMBER  I 

FIGURE  156.  —  PATH  OF  EARTH  AROUND 
THE  SUN. 


TIME  AND  SEASONS 


213 


of  day  and  night  starting  with  June  22,  as  the  earth  revolves 
around  the  sun. 

Problem  2.  Why  July  and  August  are  the  hottest  months 
and  January  the  coldest  month.  —  According  to  the  amount 
of  heat  received  from  the  sun,  what  days  of  the  year  would 
you  expect  to  be  the  hottest?  Which  is  the  chief  source  of 
heat  of  the  air,  the  direct  rays  of  the  sun,  or  the  heat  given 


TEMP 


•MO" 


-20' 


-40' 


-60' 


Jan. 


Feb. 


Mar 


dpr. 


May  Jutie  Ju/y 


5ept 


Oct. 


Nov. 


Dec. 


TEMP. 
FAHFb 

+80 
+60 


+2* 


0' 


FIGURE  157.  —  ANNUAL  TEMPERATURE  CURVES. 

Average  annual  temperature  curves  of  two  inland  places  and  two 
places  located  near  the  ocean.  Compare  the  maximum  average  summer 

temperatures. 

out  by  the  land  and  water  of  the  earth's  surface?  (Of 
course,  they  too  have  received  their  heat  from  the  sun.) 
What  becomes  of  a  large  amount  of  the  heat  which  comes 
from  the  sun  during  the  latter  half  of  June?  What  finally 
becomes  of  much  of  thi^  heat  ? 


214  GENERAL   SCIENCE 

It  takes  a  considerable  time  to  heat  the  land  and  water, 
and  on  the  other  hand  they  cool  off  gradually.  Explain 
why  January  is  colder  than  the  latter  half  of  December. 
You  have  already  learned  that  bodies  of  land  cool  more 
rapidly  than  bodies  of  water.  Explain,  therefore,  why  coast 
cities  have  a  later  spring  and  winter  than  inland  cities 
(Figure  157). 

Why  is  the  strip  of  land  about  ten  miles  wide  along  Lake 
Ontario  the  best  peach-producing  region  of  New  York  ? 

Problem  3.  How  time  is  calculated.  —  Some  of  us  must 
have  been  surprised  when  we  received  news  of  the  signing 
of  the  Peace  Treaty  before  the  time  scheduled  for  the  event 
to  occur  in  Paris.  Then  we  were  told  that  the  time  at  Paris 
was  five  hours  faster  than  our  own  time;  that  when  it  is 
noon  at  Paris,  our  7  o'clock  morning  whistles  are  blowing; 
and  when  we  stop  work  for  luncheon,  the  people  of  Paris 
and  London  are  ready  to  quit  work  for  the  day,  as  it  is  5  P.M. 
with  them. 

The  general  difference  in  time  between  different  places 
may  easily  be  understood  when  we  consider  that  one  com- 
plete rotation  of  the  earth  makes  one  day  of  24  hours,  and 
that  noon  by  sun  time  at  any  place  is  the  time  when  the 
sun  is  directly  over  a  north  and  south  line  running  through 
that  place.  In  what  direction  does  the  earth  rotate? 
In  which  city,  New  York  or  San  Francisco,  will  12  noon 
of  a  certain  day  first  occur  ? 

For  convenience  in  comparing  times  and  for  the  pur- 
pose of  locating  places  on  the  earth's  surface,  imaginary 
lines  (meridians)  are  supposed  to  be  drawn  around  the  earth 
from  pole  to  pole  (Figure  158).  There  are  360  of  these 
equally  distant  from  one  another.  Why  360  ?  The  distance 
between  these  lines  is  called  a  degree  of  longitude.  Is  a  de- 


TIME  AND  SEASONS 


215 


gree  of  longitude  always  of  the  same  length  in  miles?  At 
the  equator  a  degree  of  longitude  measures  about  69  miles. 
How  much  does  a  degree  of  longitude  measure  in  miles  at 
the  poles?  Usually  the  meridian  passing  through  Green- 
wich, England,  is  called  zero,  and  longitude  is  stated  as  east 
or  west  of  Greenwich. 

Since  the  earth  rotates  on  its  axis  once  in  24  hours,  how 
many  degrees  of  longitude  will  pass 
under  the  sun  in  an  hour  ?  Thus, 
for  every  15°  of  longitude,  the 
sun  time  of  two  places  differs  one 
hour.  If  our  clocks  were  set 
strictly  by  sun  time,  what  would 
be  true  of  the  clock  time  of  every 
place  east  and  west  of  a  given 
place?  In  what  way  would  this 
be  inconvenient? 

To    prevent   the    trouble    and 
annoyance    arising    from   such   a 

condition,  the  United  States  Government  in  1883,  at  the 
suggestion  of  the  American  Railway  Association,  adopted 
standard  time.  By  this  arrangement  the  time  of  the 
following  meridians,  75th,  90th,  105th,  and  120th,  were 
taken  as  standards  of  time  called  Eastern,  Central,  Moun- 
tain, and  Pacific  Time.  The  area  of  the  country  to  which 
the  time  was  assigned  extended  approximately  1\  degrees 
on  each  side  of  the  standard  meridian;  the  exact  division 
being  determined  largely  by  the  location  of  important  cities 
(Figure  159).  As  a  result,  in  going  from  New  York  to 
Chicago,  we  need  to  change  our  watches  only  once.  Should 
the  hands  of  the  watch  be  advanced  or  turned  back  ?  How 
much? 


FIGURE  158.  —  LINES  OF  LATI- 
TUDE AND  LONGITUDE. 


216 


GENERAL   SCIENCE 


Daylight  saving.  — On.  March  19,  1918,  President  Wil- 
son approved  a  bill  passed  by  Congress,  by  which  the  stand- 
ard time  throughout  the  United  States  was  advanced  one 
hour  for  the  period  beginning  at  2  A.M.  on  the  last  Sunday  in 
March  and  ending  at  2  A.M.  on  the  last  Sunday  in  October. 
Suggest  advantages  of  this  bill  to  the  various  classes  of 
people  of  your  community.  Does  it  seem  to  work  a  hard- 
ship to  any?  During  the  summer  of  1919,  because  of  ob- 


FIGURE  159.  —  STANDARD  TIME  BELTS. 

jection  to  the  daylight-saving  plan  by   various   interests 
of  the  country,  Congress  repealed  the  bill. 

The  movement  originated  in  England  in  1907.  It  was 
not  until  1916,  however,  that  definite  action  was  taken,  when 
within  three  months  daylight  saving  was  adopted  in  Eng- 
land, France,  Italy,  Norway,  Sweden,  Denmark,  Switzer- 
land, Spain,  Portugal,  Holland,  Germany,  Austria,  and  Tur- 
key. Practically  no  confusion  resulted;  everything  went 
on  as  before,  people  doing  exactly  the  same  things  at  the 


TIME  AND    SEASONS  217 

same  time  by  the  clock,  but  in  reality  the  whole  routine  of 
life  had  been  brought  one  hour  nearer  sunrise.  The  scheme 
had  brought  about  in  the  simplest  way  a  vital  change  affect- 
ing millions.  A  simple  "  twist  of  the  wrist  "  had  given  these 
nations  their  "  place  in  the  sun."  Friends  of  the  movement 
in  America  claim  that  the  annual  conservation  of  coal  in  the 
United  States  would  amount  to  no  less  a  sum  than  $40,000,- 
000  per  season. 

Problem  4.  How  places  on  the  earth's  surface  are  in- 
dicated. —  A  ship  having  become  disabled  at  sea  needs 
help.  It  has  a  wireless  outfit  for  calling  assistance,  but 
how  is  it  to  indicate  its  position  to  the  rescuing  ship  ?  Winds 
and  currents  may  have  carried  it  far  out  of  its  course.  Evi- 
dently it  is  impossible  to  give  its  location  by  stating  its 
position  in  miles  from  certain  points.  The  officer  in  charge, 
by  noting  the  difference  between  his  sun  time  and  the  time 
registered  by  his  chronometer  (a  very  accurate  clock)  giv- 
ing the  time  at  Greenwich,  is  able  to  determine  his  position 
in  degrees  of  longitude,  east  or  west  of  Greenwich.  Vessels 
within  reach  of  wireless  stations  receive  daily  the  correct 
Greenwich  time.  This  is  more  satisfactory  than  depend- 
ence on  chronometers.  Why?  The  north  and  south  posi- 
tion is  determined,  by  comparing  the  height  above  the 
horizon  of  a  known  fixed  star  as  it  crosses  the  meridian, 
with  tables  in  his  nautical  almanac  giving  the  height  of 
this  star  above  the  horizon  at  different  distances  from  the 
equator. 

For  example,  where  would  the  Pole  Star  appear  to  you  if 
you  were  at  the  North  Pole?  Where  would  it  appear  to 
you  if  you  were  at  the  Equator?  If  you  should  travel 
from  the  Equator  to  the  North  Pole  how  would  the  posi- 
tion of  the  Pole  Star  seem  to  change? 


218  GENERAL  SCIENCE 

The  distance  from  the  equator  is  measured  by  degrees  of 
latitude.  The  equator  is  zero,  and  the  poles  90°.  Thus  any 
place  on  the  earth's  surface  may  be  accurately  determined 
by  giving  its  latitude  and  longitude. 

The  navigating  officer  of  a  ship  with  these  means  of  de- 
termining his  position,  by  consulting  his  charts  and  by  the 
use  of  the  compass  is  able  to  direct  his  course  with  sur- 
prising accuracy. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Chart  the  position  of  the  sun  above  the  horizon  at  a  certain  hour 
every  day  for  a  month.     Interpret  the  results. 

2.  At  a  certain  hour  one  day  each  week  determine  the  amount  of 
earth  surface  covered  by  a  column  of  sunlight  whose  cross  section  is 
one  square  foot. 

REPORTS 

1.  Make, a  chart  showing  the  relative  length  of  day  and  night 
throughout  the  year.    Accompany  this  by  a  diagram  showing  the  cause 
of  the  differences  in  the  length  of  day  and  night. 

2.  Make  a  chart  showing  the  standard  time  belts. 

3.  Give  method  of  determining  latitude  and  longitude  of  a  place. 


UNIT  IV 

WORK  AND  ENERGY 

PROJECT  XXI 
THE  SUN  AS  A  SOURCE  OF  ENERGY 

THE  question  of  energy  and  the  work  it  makes  possible 
has  been  an  important  part  of  almost  every  project  and 
problem  we  have  considered.  It  seems  wise,  however,  to 
get  together  the  knowledge  we  have  already  gained  con- 
cerning work  and  energy  and  especially  to  take  up  the  ques- 
tion of  how  man  makes  use  of  energy  to  contribute  to  his 
own  comfort  and  to  carry  on  the  work  of  the  world  As 
the  sun  has  been  frequently  mentioned  as  the  great  source 
of  energy,  our  first  project  may  well  be  the  sun. 

You  will  recall  that  we  came  to  the  conclusion  that  the 
energy  of  water  power  and  of  food  and  fuel  could  be  traced 
back  to  the  sun.  Explain,  therefore : 

(a)  The  relation  of  the  sun's  energy  to  water  power. 
Into  what  other  forms  may  the  mechanical  energy  of  water 
power  be  transformed?  (6)  How  the  energy  of  the  human 
body  may  be  traced  back  to  the  sun.  (c)  How  the  energy 
obtained  from  the  burning  of  coal  and  wood  is  really  energy 
derived  from  the  sun. 

There  is  reason  to  believe  that  petroleum  from  which 
gasoline,  kerosene,  paraffin,  and  similar  compounds  are  ob- 
tained, and  natural  gas,  which  in  many  parts  of  the  coun- 

219 


220 


GENERAL  SCIENCE 


try  is  used  for  fuel  and  lighting  purposes,  have  been  formed 
as  a  result  of  decomposition  of  animal  and  plant  deposits. 
What,  therefore,  is   the  source  of  energy  exerted  by  the 
engine  of  the  automobile  and  airplane  ? 
What  do  you  consider  to  be  the  source  of  the  energy  of 


FIGURE  160. — WINDMILL. 

The  machine  at  the  left  is  one  of  the  earliest  reapers  for  the  cutting  of 

grain. 

alcohol  which  may  become  the  great  fuel  of  the  future  if  the 
supply  of  petroleum  becomes  exhausted.  Alcohol  is  made 
by  the  action  of  yeast  upon  sugar. 

The  energy  of  winds  also  may  be  referred  back  to  the  sun's 
energy.  Wind  is  not  only  used  to  propel  ships  but  also 
to  run  windmills  which  are  used  especially  for  pumping 
water  and  grinding  grain  (Figure  160).  The  windmills  of 
Holland  are  of  considerable  historic  interest,  but  American 


THE  SUN  AS  A   SOURCE  OF  ENERGY  221 

manufacturers  are  producing  more  efficient  windmills  than 
those  of  Europe.  In  some  agricultural  districts  the  wind- 
mill is  very  generally  used  for  pumping  water,  although  in 
recent  years  it  is  being  replaced  to  a  great  extent  by  the 
gasoline  engine.  Suggest  reasons  for  this. 

Problem  1.    How  the  sun's  energy  is  used  in  making 
pictures.  —  You  "know  that  the  light  strikes  the  film  or 


FIGURE  161. — A  NEGATIVE. 

plate  which  is  coated  with  gelatine  containing  a  substance 
that  is  sensitive  to  light.  When  the  film  is  put  into  a  solu- 
tion known  as  a  developer,  a  black  precipitate  made  up  of 
minute  particles  of  silver  is  produced  wherever  the  light  has 
struck  the  film.  It  is  now  washed  in  "  hypo  "  (a  solution 
of  sodium  thiosulphate)  which  dissolves  out  the  sensitive 
compound  which  has  not  been  touched  by  the  rays  of  light. 
The  film,  on  which  the  dark  parts  of  the  object  repre- 
sented are  light  and  the  light  parts  dark,  is  now  called  a 
negative  (Figure  161).  This  may  be  placed  over  paper 


222 


GENERAL  SCIENCE 


coated  with  a  sensitive  substance  similar  to  that  on  the 
film,  arid  exposed  to  light.  The  print  which  is  produced 
has  the  light  and  dark  places  arranged  just  as  they  are  in 
the  object  (Figure  162).  Explain  why  this  is  true.  Light 
other  than  direct  sunlight  may  be  used,  but  sunlight  is  much 
more  active. 


FIGURE  162. — :  PRINT  MADE  FROM  THE  NEGATIVE  ON  PAGE  221. 

Blue  prints.  —  Blue  prints,  which  you  have  seen  con- 
tractors and  builders  consulting,  are  copies  of  architects' 
drawings  made  in  the  following  way.  The  drawing  made  in 
opaque  ink  upon  transparent  linen  paper  is  placed  over  a 
sheet  of  paper  which  is  coated  with  an  almost  colorless  sub- 
stance that  becomes  blue  when  exposed  to  the  light.  The 
print  is  then  washed  in  water  and  the  positions  of  the  opaque 
ink  lines  appear  white  while  all  the  remaining  portion  of  the 
paper  is  blue. 

You  will  recall  from  your  study  of  oxidation  that  a  change 
in  which  a  new  kind  of  a  substance  is  produced  is  called  a 


THE  SUN  AS  A   SOURCE  OF  ENERGY  223 

Chemical  change.  It  is  evident,  therefore,  that  the  changes 
produced  by  the  sunlight  in  making  pictures  and  blue  prints 
are  chemical  changes. 

Problem  2.  Other  chemical  changes  produced  by  the 
sun's  energy. — The  power  of  the  sun's  rays  to  produce 
what  we  call  chemical  changes,  illustrated  in  the  making  of 
starch  in  plants  and  in  the  making  of  pictures,  is  also  shown 
by  some  rather  common  phenomena,  (a)  Fading  of  colors.  — 
(1)  What  is  the  appearance  of  portions  of  wall  paper  which 
have  been  covered  by  pictures  as  compared  with  the  re- 
maining part  of  the  wall  ?  (2)  What  is  the  appearance  of 
your  straw  hat  after  it  has  been  worn  in  the  sunlight  for 
several  weeks?  (3)  Give  other  examples  of  changes  of  this 
kind  which  you  have  noticed. 

(b)  Action  upon  living  animals  and  plants.  —  (1)  What 
is  the  effect  of  the  sun  upon  the  skin  ?  Will  light  of  a  gas  or 
electric  lamp,  or  heat  of  a  stove  or  furnace,  produce  the  same 
changes?  (2)  What  is  the  effect  of  exposing  to  the  sunlight 
parts  of  a  plant  that  have  been  kept  in  darkness,  as  a  potato 
or  a  stalk  of  bleached  celery  ?  (3)  What  is  the  effect  of  sun- 
light upon  bacteria  ?  This  is  the  result  of  a  chemical  change 
in  the  living  matter. 

Problem  3.  How  direct  use  may  be  made  of  the  sun's 
energy.  —  (a)  Cold  frame  and  sun  parlor.  —  A  large  part 
of  the  sun's  energy  is  turned  into  heat  when  it  strikes 
the  earth.  Much  of  this  energy  radiates  back  into  space, 
and  while  it  is  considered  that  no  energy  can  be  destroyed, 
yet  so  far  as  its  utility  to  us  on  the  earth  is  concerned,  it  is 
lost.  The  effect  of  clouds  in  preventing  the  direct  escape  of 
this  energy  into  space  has  been  touched  upon  elsewhere. 

The  cold  frame  and  sun  parlor  are  other  examples  of  the 
capture  of  this  energy  (Figure  163).  In  both  of  these  cases 


224 


GENERAL   SCIENCE 


rays  of  the  sun,  in  the  form  of  light,  pass  through  the  glass ; 

but  the  heat  into  which  it  is  changed  does  not  pass  through 

the  glass  easily,  and  as  a  result 
the  space  inclosed  in  the  glass 
becomes  considerably  warmer  than 

FIGURE  163.-^- COLD  FRAME.      -  ,    .,       ,. 

the  outside  air. 

(b)  Solar  engines.  —  We  sometimes  wonder  what  the 
world  will  do  for  its  supply  of  usable  energy  after  the  coal 
and  oil  deposits  have  been  exhausted.  Here  we  have  sug- 
gested one  possible  solution.  If  the  energy  which  is  radiating 
into  space  could  be  caught  and  used,  all  demands  of  energy 
for  light,  heat,  and  power  would  be  met.  The  amount  of 
this  energy  is  enormous;  it  has  been  calculated  that  the 
amount  of  energy  of 
the  sun's  rays  falling 
upon  the  deck  of  a 
ship  when  the  sun 
is  directly  overhead, 
if  turned  into  work 
without  loss,  would 
be  sufficient  to  drive 
the  vessel  at  a  fair 
rate  of  speed. 

Efforts  have  been 
made  to  develop  a 
solar  engine  by  which 
this  energy  which  now 
is  lost  to  us  might  be  FlGURE  164.— SOLAR  ENGINE. 

applied  to  practical  uses.  In  California,  by  means  of  great 
reflectors,  the  sun's  rays  were  thrown  upon  the  surface  of  a 
boiler  composed  of  a  coil  of  blackened  copper  tubing  (Figure 
164).  Sufficient  heat  was  developed  to  run  an  engine  which 


THE  SUN  AS  A   SOURCE  OF  ENERGY  225 

pumped  water  for  irrigation  purposes.  The  cost  of  the 
power,  however,  because  of  expense  of  construction  and 
repairs,  was  much  greater  than  if  an  ordinary  engine  had 
been  used. 

Other  plants  have  been  constructed  in  which  the  sun's 
rays  were  permitted  to  fall  upon  a  series  of  shallow  trays 
whose  sides  and  bottoms  were  made  of  a  substance  which  is 
a  poor  conductor  of  heat.  The  trays  were  covered  with  a 
double  layer  of  glass  which  acted  in  the  same  way  as  the 
glass  cover  of  a  cold  frame  or  sun  parlor.  Explain.  A  thin 
layer  of  water  which  flowed  through  the  trays  absorbed  the 
heat. 

The  most  successful  plants  for  the  direct  use  of  solar  energy 
have  been  constructed  in  northern  Africa.  Suggest  a  reason 
for  this.  Unfortunately,  however,  regions  of  this  kind  are 
not  apt  to  become  centers  of  industry.  Why?  This  objec- 
tion is  now  overcome  to  a  great  extent  by  the  development 
of  methods  of  transmission  of  electric  power. 

Problem  4.  How  the  energy  of  the  sun  is  maintained.  — 
From  what  has  been  said  in  this  chapter,  what  is  your  con- 
clusion as  to  the  source  of  all  heat,  light,  and  activity  upon 
the  earth  ?  If  the  sun  should  become  cold,  do  you  think  that 
the  earth  would  continue  to  revolve  around  it,  and  rotate 
upon  its  own  axis?  Would  the  moon  revolve  around  the 
earth?  Would  there  be  any  seasons?  Explain  your 
answers. 

This  sun  to  which  we  owe  so  much  has  a  diameter  a  hun- 
dred times  greater  than  that  of  the  earth,  but  it  is  located 
92,000,000  miles  from  us.  Evidently  the  earth  receives  an 
extremely  small  amount  of  the  total  energy  sent  out  by  the 
sun.  This  amount  has  been  calculated  to  be  about  1  part 
in  2,000,000,000.  Although  the  amount  of  energy  that  is 


226  GENERAL   SCIENCE 

being  given  off  is  almost  beyond  our  imagination,  yet  there 
seems  to  be  no  lessening  of  it.  Scientists  believe  that  the 
undiminished  supply  is  maintained  by  the  heat  and  light 
which  are  produced  as  the  particles  that  make  up  the  sun, 
which  is  less  solid  than  the  earth,  are  drawn  toward  its  center 
by  the  force  of  gravitation;  the  energy  of  gravitation  being 
changed  into  radiant  energy. 

Therefore,  it  is  believed  that  at  present  the  radiant  energy 
produced  by  contraction  is  equal  to  the  amount  of  energy 
continually  being  given  off  by  the  sun.  Of  course,  this  can- 
not keep  on  forever,  and  in  some  future  period,  perhaps 
millions  of  years  from  now,  the  loss  of  energy  from  the  sun 
will  exceed  the  supply  resulting  from  contraction,  and  the 
sun  with  its  planets  will  gradually  become  dark  and  cold. 


SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Make  a  collection  of  articles  showing  the  effect  of  the  sun  in 
causing  colors  to  fade.     Do  any  colors  seem  to  be  especially  resistant 
to  the  action  of  the  sun  ? 

2.  Demonstrate  the  process  of  making  a  photographic  negative. 

3.  Demonstrate  the  process  of  making  photographic  prints. 

4.  Draw  plans  for  something  that  you  want  to  make,  and  make  blue 
print  copies  of  it. 

5.  Make  a  cold  frame  and  use  it  in  growing  plants. 

6.  Make  a  sailboat  and  demonstrate  how  the  wind  makes  it  go  in 
different  directions. 


REPORTS 

1.  Write  a  brief  history  of  the  development  of  photography. 

2.  Describe  efforts  that  have  been  made  to  make  direct  use  of  the 
energy  of  the  sun  by  means  of  solar  engines. 


THE  SUN  AS  A   SOURCE  OF  ENERGY  227 

REFERENCES  FOR  PROJECT  XXI 

1.  How  to  Make  Good  Pictures,  Eastman  Kodak  Co.    Rochester, 
New  York. 

2.  Something  to  Do,  Boys,  E.  A.  Foster.    W.  A.  Wilde  &  Co. 

3.  Harper's  Machinery  Book  for  Boys,  Adams.     Harper  &  Bros. 
(Sun-power.) 

4.  All  About  Engineering,  Knox.     Funk  &  Wagnalls.     (Power  and 
Its  Source.) 

5.  Boy's  Book  of  Inventions,  Doubleday,  Page  &  Co.     (Harnessing 
the  Sun.) 


PROJECT   XXII 
MACHINES 

DURING  the  earliest  periods  of  which  we  have  any  record, 
the  earth  was  receiving  just  as  much  energy  from  the  sun 
as  at  present.  Little  use,  however,  was  made  of  this  energy 
as  compared  with  the  present  times.  As  man  discovered 
the  use  of  tools  and  then  machines,  civilization  advanced. 
This  is  now  an  age  of  machinery.  How  man  has  multi- 
plied his  ablities  by  the  use  of  machines  is  the  project  we 
have  for  solution. 

Before  we  can  understand  how  machines  have  enabled 
man  to  do  much  more  than  he  could  with  his  unaided  hand, 
the  meaning  of  several  terms  which  have  been  used  inci- 
dentally a  number  of  times  must  be  clearly  understood. 

Problem  1.  What  is  meant  by  work  and  force.  —  We 
have  already  defined  energy  as  the  power  to  do  work,  but  just 
what  do  we  mean  by  doing  work?  A  man  who  digs  a  ditch 
or  shovels  coal  is  doing  work.  Steam  which  moves  a  piston, 
which  in  turn  operates  a  pump,  which  lifts  water  to  a  tank 
on  the  roof,  does  work.  This  water  in  turn,  we  know,  as  it 
descends  may  operate  a  motor  which  will  run  a  sewing  ma- 
chine or  a  churn,  or  may  generate  electricity  which  may 
run  a  motor,  or  be  changed  into  heat  to  be  used  again  in  boil- 
ing water  to  produce  steam.  In  raising  the  water,  work  is 
being  done ;  also  in  the  movement  of  the  parts  of  the  sew- 
ing machine  or  churn  or  dynamo,  work  is  being  done. 

The  essential  of  all  these  examples  of  work  is  that  there  is 

228 


MACHINES  229 

the  movement  of  a  material  thing  through  space  against  some 
resistance.  What  is  the  resistance  that  is  overcome  in 
lifting  the  water  to  the  roof?  In  the  sewing  machine  it  is 
the  inertia  (the  tending  of  a  body  to  remain  in  the  condi- 
tion in  which  it  is),  the  friction  of  the  parts  of  the  machine, 
and  the  friction  of  the  needle  as  it  passes  through  the  cloth. 
In  the  same  way,  the  electricity  in  moving  the  parts  of  the 
motor  against  resistance  is  doing  work. 

A  boy  who  lifts  a  ten-pound  weight  from  the  floor  to  a 
table  is  doing  work.  If  the  boy  holds  the  weight  he  is  doing 
no  work,  although  the  muscles  of  his  arms  may  become  very 
tired.  He  is,  however,  exerting  sufficient  force  to  resist  the 
force  of  gravity  upon  the  ten-pound  body.  Since  the  body 
is  neither  raised  nor  lowered,  the  force  he  is  ex- 
erting must  be  equal  to  the  amount  of  the  pull 
of  gravity  upon  it. 

Problem  2.  How  work  and  force  are  meas- 
ured. —  We  measure  forces  in  terms  of  pounds 
or  grams  of  force.  The  weight  of  a  body  is  the 
measure  of  the  force  of  gravity  upon  it.  Force, 
however,  may  be  exerted  in  many  directions. 
An  easy  method  of  measuring  a  force  is  by  the 
use  of  a  spring  balance  (Figure  165).  Work 
considers  the  distance  through  which  the  force  FIGURE  165. 

is  acting.    This  may  be  well  illustrated  in  the    ~T  SPRING 
•  „      .  BALANCE. 

following  way. 

Experiment.  —  Attach  a  spring  balance  to  a  weight ;  pull  on  the 
balance  until  the  weight  moves,  noting  the  number  of  pounds  of  force 
represented  by  the  pointer.  Suppose  the  pointer  registers  one  pound 
of  force;  now  pull  the  weight  along  one  foot.  The  amount  of  work 
which  is  done  is  called  one  foot-pound.  If  the  weight  is  moved  two 
feet,  two  foot-pounds  of  work  are  performed.  If  the  force  necessary 


230  GENERAL   SCIENCE 

to  move  a  larger  weight  is  two  pounds,  then  the  amount  of  work  done 
in  moving  it  one  foot  is  two  foot-pounds. 

Time  is  not  a  factor  in  considering  work  done.  Whether 
it  takes  one  minute  or  a  year  to  move  an  object  a  certain 
distance  against  a  uniform  resistance,  the  amount  of  work 
done  is  the  same.  You  know  that  whether  a  man  takes  an 
hour  or  two  days  to  shovel  a  ton  of  coal  from  one  place  to 
another,  the  work  done  is  the  same. 

The  rate  of  work  is  measured  in  the  terms  of  horse  power. 
This  unit  was  chosen  and  named  by  James  Watt  who  did  so 
much  for  the  development  of  the  steam  engine.  A  horse 
power  was  supposed  to  be  the  rate  at  which  an  average 
horse  works.  A  machine  of  one  horse  power  is  able  to  do 
33,000  foot-pounds  of  work  per  minute  or  550  foot-pounds 
per  second. 

Problem  3.  Reasons  for  using  machines.  —  A  device 
by  which  forces  are  advantageously  applied  to  accomplish 
work  desired  is  called  a  machine.  Name  the  machines 
with  which  you  are  most  familiar,  and  state  the  purpose  of 
each.  Explain,  as  far  as  possible,  how  the  invention  of  these 
machines  has  resulted  in  the  accomplishment  of  a  greater 
amount  of,  or  more  satisfactory,  work.  The  chief  advantages 
gained  in  the  use  of  machines  may  be  made  clear  by  a  few 
simple  examples. 

(a)  What  is  the  advantage  of  a  claw 
hammer  in  pulling  out  a  nail  (Figure  166)  ? 
Can  you  exert  sufficient  force  with  the 
fingers  to  pull  the  nail  ?  .  Give  other  exam- 
ples showing  that  by  use  of  a  machine 
greater  force  may  be  exerted  at  a  parti- 
cular point. 
(6)  What  are  the  advantages  gained  in  the  use  of  a  sew- 


MACHINES  231 

ing  machine?  Why  does  a  country  doctor  use  an  auto- 
mobile instead  of  a  horse  and  buggy  as  formerly?  Give 
other  examples  showing  how  speed  is  gained  by  the  use  of 
machines. 

(c)  What  is  the  advantage  of  using  a  single  fixed  pulley, 
as  in  raising  a  flag  to  the  top  of  a  flagpole?  Give  other 
examples  in  which  an  advantage  is  gained  by  changing  the 
direction  of  the  force. 

Complex  machines.  —  Most  machines,  such  as  a  sewing 
machine,  typewriter,  clock,  automobile,  or  threshing  ma- 
chine, are  so  complex  that,  at  first  sight,  to  gain  an  under- 
standing of  their  mechanism  seems  almost  an  endless  task. 
It  will  be  found,  however,  that  each  of  these  machines  is  a 
combination  of  a  large  number  of  simple  machines  which 
can  easily  be  understood.  These  simple  machines  are  the 
lever,  the  wheel  and  axle,  the  pulley,  the  inclined  plane, 
the  wedge,  and  the  screw. 

Problem  4.  How  the  lever  is  used  in  doing  work.  — 
1.  Let  us  suppose  that  a  heavy  rock  must  be  lifted,  and  we 
find  that  we  are  unable  to  do  it  by  hand.  By  the  use  of  a 
strong  beam  or  a  crowbar  (a  strong 
steel  bar)  in  the  way  indicated  in  the 
diagram,  the  lifting  is  accomplished 

•j.i_  TXJ.I     J'/T?      ij_    /TV  -tr»-r\  FIGURE    167.  —  CROWBAR. 

with  little  difficulty  (Figure  167). 

The  bar  constitutes  a  lever;  the  point  on  which  it  rests 
is  the  fulcrum,  and  the  portions  of  the  bar  on  either  side 
of  the  fulcrum  are  the  arms.  The  amount  of  force  that 
must  be  applied  may  be  determined  by  the  following  ex- 
periment. 

Experiment.  —  Use  a  yard  or  meter  stick  as  the  lever ;  use  a  10- 
pound  weight,  placing  the  lever  on  the  fulcrum  in  such  a  way  that 
one  arm  is  ten  times  as  long  as  the  other.  Place  small  weights  on  the 


232  GENERAL  SCIENCE 

end  of  the  long  arm  until  the  lever  balances  on  the  fulcrum  and  the 
weight  is  lifted  from  the  table.  What  weights  have  you  placed  on  the 
long  arm  ?  Vary  the  experiment  by  putting  the  fulcrum  at  different 
places,  thus  changing  the  relative  length  of  the  arms. 

It  will  be  noted  that  the  force  needed  to  lift  the  weight 
is  inversely  proportional  to  the  length  of  the  arms.  There- 
fore 

effort  X  its  arm  =  weight  or  resistance  X  its  arm. 

The  slight  variations  from  this  are  due  to  the  weight  of 
the  lever,  and  the  small  amount  of  friction  between  the 
lever  and  fulcrum.  Measure  the  distance 
through  which  each  arm  moves.  What  are 
your  conclusions?  Compare  the  amount  of 
work  done  at  the  end  of  each 
arm. 

This  experiment  is  duplicated 
in  the  action  of  the  seesaw  which 
most  of  you  have  tried.   What  is         FIGURE  169. 
the  position  of  a  heavy  boy  and         —SCISSORS. 
FIGURE "TeS.  ^hat  °^  a  nSn^  boy?      Compare       Why   is  the  cord 

-TONGS.  '  the  distances  through  which  each  not  cut  b^  thf  end  of 

.  the  scissors  ? 

Why  such  a  moves.    Give  all  the  uses  you 

long  handle?  ^  ^  ^^  Q{  ^  kind    (pjg- 

ures  168  and  169).  These  are  called  levers  of  the  first  class. 
2.  Considering  the  wheelbarrow  as  a  lever,  where  is  the 
fulcrum,  the  resistance  or  weight,  and  the  effort  or  power? 
Why  is  it  easier  to  lift  a  bag  of  flour  in  a  wheelbarrow  than 
directly  by  hand  ?  Would  making  the  handles  longer  cause 
it  to  be  harder  or  easier  to  lift  the  load  ?  Why  are  the  handles 
not  made  longer  ?  Give  other  examples  of  levers  with  the 
same  relative  arrangement  of  fulcrum,  resistance  or  weight, 
and  the  effort  or  power  (Figure  170).  In  these  levers 


MACHINES  233 

compare  the  length  of  the  power  arm  and  the  entire  lever. 
These  are  called  levers  of  the  second  class. 

3.  Considering  a  pitchfork  or  a  fishing  pole  as  a  lever, 
where  is  the  fulcrum,  the  resistance  or 

weight,  and  effort  or  power?     What  is 
the  advantage  in  using  such  a  lever? 

In  using  a  pole  10  feet  long,  about  how        FlGURE  170-- 

°  NUTCRACKER. 

much  force  must  be  used  to  land  a  fish 

weighing  5  pounds?  What  are  the  advantages  and  dis- 
advantages of  using  a  very  long  handled  pitchfork?  Give 
other  examples  of  levers  of  this  kind.  They  are  called  levers 
of  the  third  class. 

4.  Explain  how  the  bones  of  the  human  body  act  as  levers 
during  walking,  running,  lifting,  and  throwing  (Figure  171). 
To  which  class  of  levers  do  they  belong  ? 

Problem  5.  How  wheels  are  used  in  doing  work. — 
Wheels  are  so  commonly  used  in  machines  that  when  most 

of  us  think  of  machines  and 
machinery,  we  also  think  of 
wheels.  Like  the  lever,  they 
may  be  used  to  gain  force  at 
the  expense  of  distance  or 
FIGURE  171.— ARM  AS  A  LEVER,  speed,  or  may  be  used  to  ob- 

Estimate  force  necessary  to  lift  a    tain  speed  or  distance  at  the 

10-pound  weight.  „    „  . 

expense  of  force,  or  may  be 

used  to  change  the  direction  of  the  action  of  a  force  as  in 
the  beveled  cogwheels  used  in  transmitting  the  power  of  the 
crank  shaft  to  the  inner  axle  which  turns  the  wheels  of  an 
automobile. 

1.  The  windlass.  —  One  of  the  most  easily  understood 
examples  of  the  action  of  the  wheel  and  axle  is  the  case  of 
the  windlass  which  is  used  to  draw  water  from  a  well,  raise 


234  GENERAL   SCIENCE 

the  anchor  of  a  ship,  or  move  buildings  (Figure  172).  Most 
of  us  have  seen  the  delivery  man  on  a  coal  wagon  raising 
the  bed  of  the  wagon  containing  several  tons  of  coal  by 
turning  a  crank  at  the  side  of  it.  It 
does  not  seem  difficult,  although  he  is 
raising  a  weight  many  times  greater 
than  he  would  be  able  to  lift  unaided. 
The  reason  for  the  use  of  the  crank, 
which  is  really  only  a  spoke  of  a  large 
wheel,  may  be  understood  by  considering 
it  as  a  lever. 

FIGURE  172.— WELL        Comparing  this  with  a  lever,  what  may 

WINDLASS.  ,  .  .      &. 

be  considered  to  be  the  fulcrum,  what 
the  power  arm,  and  what  the  weight  or  resistance  arm? 
Explain  the  advantage  in  the  use  of  the  windlass,  and  its 
modifications  in  pulling  or  lifting  heavy  weights.  Explain 
the  ease  with  which  the  grains  of  coffee  are  crushed  by 
the  hand  coffee  grinder,  and  with  which  meat  is  chopped  by 
the  kitchen  meat  chopper. 

2.  Cogwheels  and  wheels  moved  by  belts.  —  In  machines 
much  use  is  made  of  cogwheels.  With  these,  as  with 
other  simple  machines,  power  may  be  gained  at  the  ex- 
pense of  speed,  or  speed  may  be  gained  at  the  expense  of 
power.  The  high  and  low  speeds  of  the  automobile  illus- 
trate this  fact  very  well.  Along  the  level  road  the  car  runs 
in  high  gear ;  but  as  soon  as  it  begins  to  climb  a  steep  hill, 
the  driver,  by  means  of  a  lever  at  his  side,  shifts  the  gears 
so  that  a  different  cogwheel  (a  smaller  one)  engages  the 
crank  shaft.  The  machine  now  has  greater  power,  but  less 
speed.  Most  automobiles  have  three  speeds ;  first,  second, 
and  third,  and  the  force  exerted  by  the  machine  is  in  inverse 
ratio  to  the  speed. 


MACHINES  235 

With  an  apparatus  such  as  shown  in  the  diagram  (Figure 
173),  state  how  much  force  must  be  applied  on  the  crank 
to  exert  a  pull  of  2000  pounds. 

In  bicycles  and  in  some  motor  trucks,  a  chain  is  used  to 
transfer  the  power  exerted  by  the  pedals  upon  the  sprocket 
wheel  to  the  axle  of  the  rear 
drive  wheel.  In  this  case  as  in 
cases  of  cogwheels  that  are  in 
contact  or  mesh  directly,  the 
greater  the  size  of  the  sprocket 
wheel,  the  greater  the  speed 
the  machine  possesses,  with, 
however,  correspondingly  less 
power  to  climb  hills. 

Belts    are    very    commonly 
used     in    factories    to     convey    FIGURE  1 73.  —  PART  OF  A  DERRICK. 
power     to      machines.       By      a      Combination  of  wheel  and  axle 
graduated  series  of  wheels,  the 

speed  and  the  force  exerted  by  the  machine  may  be  regu- 
lated. A  very  simple  example  is  seen  in  the  foot  power 
sewing  machine.  The  heavy  rim  of  the  small  wheel,  be- 
cause of  its  inertia  (the  tendency  of  a  body  to  remain  in 
the  condition  of  rest  or  motion  in  which  it  is),  makes  the 
running  of  the  machine  much  more  even,  just  as  does  the 
flywheel  on  an  automobile. 

Why  is  the  belt  wheel  on  an  engine  that  runs  a  thresh- 
ing machine  large,  while  the  belt  wheel  of  the  threshing 
machine  itself  is  small?  Belts  are  able  to  move  the  wheels 
because  of  friction  between  the  belt  and  the  wheel. 

Problem  6.  Why  pulleys  are  used.  —  We  can  raise  a 
window  fitted  with  weights  any  distance  and  it  stays  there. 
The  pulley  reduces  the  friction.  If  the  cord  supporting 


236 


GENERAL  SCIENCE 


FIGURE  174.  —  PLACING  HEAVY  PIPE  IN  POSITION. 
Use  of  block  and  tackle  in  putting  in  place  heavy  steel  pipe,  in  con- 
struction of  an  aqueduct.     The  portion  of  the  aqueduct  shown  here 
constitutes  a  siphon  by  which  water  is  carried  over  the  hill  in  the 
background. 

the  weight  ran  through  the  opening  in  the  window  casing, 
without  the  pulley,  would  the  window  move  so  easily,  and 
what  would  be  the  condition  of  the  rope  and  the  edge  of  the 


MACHINES 


237 


opening  in  a  short  time?  Frequently,  clothes  lines  extend 
from  windows  of  an  apartment  building  to  a  pole  or  to  the 
opposite  side  of  a  courtyard.  Explain  how  the  clothes 
may  be  hung  on  the  line  for  its  whole  length  though  it  is  far 
above  the  ground.  What  is  the  advantage  of  using  a  pulley 
in  this  case?  Explain  the  importance  of  a  pulley  in  rais- 
ing a  flag  to  the  top  of  a  pole.  If  a  pulley  were  not  used, 
how  could  the  flag  be  placed  in  position?  In  these  cases 
where  a  single  fixed  pulley  is  used,  is  there  any  gain  in  force 
applied  or  distance  covered  ? 

Use  of  pulleys  in  hoisting  heavy  objects.  —  We  have 
all  seen  pianos  being  raised  to  the  upper  windows  of  build- 
ings. It  seems  rather  easy,  one  man  being  able  to  raise  one, 
although  we  know  that  lifting  a  piano  is  difficult  even  for 
several  men,  without  some  kind  of  apparatus.  In  the 
same  way,  heavy  blocks  of  stone  or  steel  girders  are  lifted 
into  place  during  the  construction  of  a  building  (Figure 
174).  Observation  will  show  that  pulleys  are  used,  usually 
in  the  form  of  what  is  known  as  a  block 
and  tackle.  The  value  of  the  pulley  can 
be  understood  by  an  examination  of  the 
diagrams  and  by  a  few  experiments. 

Experiments.  —  (a)  In  both  A  and  B  (Figure 
175)  if  the  weight  is  10  pounds,  what  does  the 
spring  balance  register?  To  raise  the  weight  6 
inches,  how  far  must  the  cord  to  which  the  spring 
balance  is  attached  be  pulled?  In  this  respect 
compare  work  done  by  pulley  with  work  done 
by  lever,  and  by  wheel  and  axle.  What  is  the  A. 
purpose  of  using  the  fixed  pulley?  FIGURE  175. 

(6)  In  the  block  and  tackle  represented  in  Figure  176,  how  many 
sets  of  pulleys  are  there?  How  much  force  must  be  exerted  in  using 
this  machine  to  lift  a  weight  of  300  pounds  if  the  weight  of  the  pulley 


238 


GENERAL   SCIENCE 


itself  is  ignored  ?  How  far  will  the  rope  have  to  be  pulled  to  lift  the 
weight  10  feet?  In  lifting  heavy  weights,  the  power  rope  is  usually 
connected  with  a  wheel  and  axle.  Explain 
the  reason  for  this.  Where  have  you  seen  sets 
of  pulleys  such  as  this  used  ? 

Problem  7.  How  inclined  planes  are 
used  in  doing  work.  —  Which  seems  to 
demand  more  effort;  walking  to  the  top 
of  a  hill  up  a  gradual  slope,  or  up  a  very 
steep  one?  In  parks  which  have  hills, 
how  are  the  paths  laid  out?  In  going  up 
mountains,  railroads  take  a  very  winding 
or  zigzag  course  instead  of  going  directly 
up.  Wagon  and  automobile  roads  are 
built  in  the  same  way  where  a  consider- 
able elevation  is  to  be  reached  (Figure 
177).  An  automobile  which  fails  to  go  to 
the  top  of  a  hill  at  high  gear,  if  the  road 
is  one  fourth  of  a  mile. long,  will  go  up 
FIGURE  176.—  easily  at  this  gear  if  the  road  is  several 

BLOCK  AND  TACKLE.     ,.  ,  T  ,.  i_        M 

times     longer.      In     pushing     a    heavily 

loaded  wheelbarrow  into  a  door  which  is  a  foot  above 
the  ground,  is  it  better  to  use  a  board  2  feet  long 
or  one  3  feet  long,  reaching  from  the  doorsill  to  the  ground  ? 

What  conclusion  do  you  draw  from  these  points  to  which 
your  attention  has  been  drawn,  and  from  other  similar 
cases  which  you  have  observed?  Evidently  in  these  cases 
as  in  the  use  of  the  lever,  the  windlass,  and  the  pulley,  in 
doing  a  specified  amount  of  work,  the  greater  the  distance 
through  which  the  force  or  effort  works,  the  less  is  the  re- 
quired effort. 

The  following  experiment  will  show  the  relation  of  effort 


MACHINES 


239 


FIGURE  177.  —  ROAD  NEAR  COLORADO  SPRINGS,  COLORADO. 

Note  the  grade  necessary  if  the  road  ran  directly  to  the  point  where 

it  disappears. 

to  length  of  the  plane  in  raising  a  weight  by  the  use  of  the 
inclined  plane. 

Experiment.  —  Take  a  smooth  board  4  feet  long ;  raise  one  end  of 
the  board  1  foot  from  the  ground  (Figure  178).  Into  a  toy  wagon 
put  weights  until  the  wagon 
and  its  contents  weigh  8  pounds ; 
attach  a  spring  balance  to  the 
front  of  the  wagon  and  by 
means  of  it  pull  the  wagon  up 
the  incline,  taking  care  to  keep 
the  spring  balance  parallel  with 
the  board.  What  does  the 
spring  balance  register?  (The 
spring  balance  will  register 
somewhat  too  high  because  of  the  friction  between  the  wheels  and 
the  board.) 

Change  the  raised  end  of  the  board  to  2  feet  above  the  ground,  and 
then  to  4  feet,  making  note  of  the  force  necessary  to  pull  the  weight 


FIGURE  178. 


240 


GENERAL  SCIENCE 


up  the  different  inclines.     Draw  your  conclusion  as  to  the  advantage 
of  the  use  of  the  inclined  plane. 

Wedges  (Figure  179),  chisels,  knives,  and  common  pins 
are  all  really  inclined  planes.  One  of  the  most  interesting 
of  modified  inclined  planes  is  the  screw  (Figure  180), 
which  has  many  uses  with  which  you  are  familiar.  All 
screws  are  inclined  planes,  as  may  be  shown  by  the  fol- 
lowing experiment. 


FIGURE  179.  —  WEDGE. 
Is  a  thick  or  a  thin  wedge  easier  to 


FIGURE  180.  — SCREW. 
How  much   is  head  of  screw 
lowered   in   complete   turn?     5, 
drive  in  ?  pitch  of  screw. 

Experiment.  —  Cut  a  piece  of  paper  into  a  right-angle   triangle, 
with  the  shorter  side  of  the  triangle  2  inches  and  the  longer  one  8  inches. 

Wind  the  paper  around  a  pencil,  begin- 
ning with  the  short  side  parallel  with  the 
pencil  (Figure  181).  What  is  the  ap- 
pearance of  the  paper  after  it  is  wound 
around  the  pencil  ? 

You     will     now 
understand  how  a 

FIGURE  181.  —  DEMONSTRATION   jackscrew     (Figure 

THAT  SCREW    Is  AN    INCLINED    10r>x         »        .  , 

PLANE  182)  is  of  assistance 

in  raising  a  build- 
ing or  a  heavy  weight,  or  how  greater  pres- 
sure may  be  brought  to  bear  by  the  use 
of  a  screw  clamp,  by  the  nut  on  a  bolt, 
or  by  presses  of  various  kinds  in 'which  FIGURE  182.— JACK- 
screws  are  used.  The  efficiency  of  the  SCREW. 


MACHINES  241 

screw  as  a  machine  is  usually  increased  by  the  use  of  a 
lever. 

Examine  various  complex  machines  and  determine  in  what 
way  these  simple  machines  are  combined,  and  the  special 
advantages  of  the  use  of  each.  \ 

Problem  8.  Why  machines  are  not  100  per  cent  efficient.  — 
Ideally,  what  should  be  the  amount  of  work  obtained  from 
a  machine  as  compared  with  the  amount  of  work  put  in? 
For  example,  with  a  block  and  tackle  such  as  represented 
in  the  figure  on  page  238,  how  many  pounds  should  you  be 
able  to  lift  by  an  exertion  of  a  force  of  50  pounds? 
Actually,  however,  you  will  be  able  to  lift  not  more  than 
60  or  75  per  cent  of  this  amount. 

In  the  same  way  you  will  find  that  the  work  obtained 
by  the  use  of  the  inclined  plane,  cogwheels,  etc.,  is  not 
equal  to  the  amount  of  work  expended.  This  is  due  to  the 
fact  that  there  is  a  certain  amount  of  resistance  when  one 
surface  slides  or  rolls  over  another.  This  resistance,  which 
is  called  friction,  results  because  the  surfaces  are  not  abso- 
lutely smooth.  Examination  with  the  microscope  will  show 
that  even  the  smoothest  appearing  surface  has  many  small 
irregularities.  Naturally,  therefore,  when  two  surfaces 
rub  together,  what  will  happen? 

The  efficiency  of  a  machine  is  the  ratio  of  the  work  done 
or  energy  given  out  to  the  work  or  energy  put  into  it.  For 
example,  if  in  the  block  and  tackle  which  we  have  con- 
sidered before,  we  pull  the  power  rope  6  feet  with  a  force  of 
50  pounds  and  are  able  to  lift  a  maximum  weight  of  200 
pounds  1  foot,  then  the  efficiency  of  the  machine  may  be 
stated  as  follows : 

vffi  •  work  done  (200X1)     200     2 

Efficlency  ~  work  put  in  (50X6)  =300"  3 


242 


GENERAL   SCIENCE 


After  using  the  pulleys  it  will  be  found  that  they  are 
slightly  warmer.  What,  therefore,  has  become  of  energy 
that  does  not  appear  as  useful  work  ? 

Problem  9.    How  friction  may  be  reduced. 

Experiment.  —  By  means  of  a  spring  balance,  pull  an  iron  block 
up  an  inclined  plane.  Note  the  pounds  of  force  necessary.  Now 
put  grease  or  heavy  oil  on  the  plane  and  on  the  lower  side  of  the  block. 
Note  again  the  force  necessary  to  pull  the  block  up  the  plane.  Con- 
clusion? 

Give  examples  of  the  use  of  oil  or  grease  in  machines  with 
which  you  are  familiar.  Explain  why  failure  to  oil  the 
working  parts  of  a  machine  will  cause  them  to  wear  out 


FIGURE  183.  —  "SKIDDING"  LOGS  ON  SNOW. 
Why  cannot  this  be  done  if  there  is  no  snow  ? 

more  rapidly;  why  screws  may  be  screwed  into  wood  more 
easily  if  soap  is  rubbed  on  them;  why  failure  of  the  oil 
supply  of  an  automobile  engine  causes  the  engine  to  become 


MACHINES 


243 


overheated;  why  the  wheel  on  a  wagon  or  automobile  will 
sometimes  refuse  to  turn  if  it  has  not  been  properly  oiled. 
(Note  that  metal  expands  when  heated.) 

Experiment.  —  By  means  of  a  spring  balance  pull  a  small  box 
filled  with  weights  or  sand  up  an  inclined  plane.  Note  the  force  re- 
quired. Now  put  rollers  under  the  box  and  again  pull  it  up  the  same 
incline.  Note  the  force  required. 

Can  you  skate  faster  with  roller  skates  fitted  with  ball 

bearings  or  with  those  which  have  plain  bearings  ?   Is  it  easier 

to  slide  a  barrel  along 

on  its  end  or  to  roll  it? 

All  automobile  and  bicy- 
cle   wheels    have    roller 

(Figure    184  a)    or    ball 

(Figure  1846)  bearings. 

What  is  your  conclusion 

concerning    the    friction 

between       surfaces      in 

Which     one     rolls     Upon  FlcuRE  ^—ROLLER  BEAHNOS. 

the  other  as  compared  with  the  friction  between  surfaces 

that  slide  upon  one  another  ?  Name  all  the  cases  you  know 
where  the  efficiency  of  machines  is  in- 
creased by  the  substitution  of  rolling 
friction  for  sliding  friction. 

Bearings  are  usually  made  of  differ- 
ent material  from  that  of  the  axles  that 
rest  upon  them.  This  is  done  because 

FIGURE  184  b.  —  BALL  generally  the  friction  between  two  sur- 
faces of  different  material  is  less  than 

that  between  surfaces  of  the  same  material. 

Problem  10.     Is  friction  ever  useful?  —  Since  we  have 

seen  how  friction  lessens  the  efficiencv  of  machines  which  we 


244  GENERAL  SCIENCE 

use  in  accomplishing  work,  we  are  likely  to  conclude  that 
friction  is  one  of  our  greatest  enemies,  and  that  our  every- 
day work  and  the  work  of  the  world  would  be  done  much 
better  if  all  friction  were  eliminated.  Let  us  see  if  this 
conclusion  is  a  correct  one. 

Let  us  suppose  that  instead  of  raising  a  piano  to  a  high 
window,  we  are  lowering  it  from  that  position ;  what  effect 
will  friction  have?  What  would  happen  to  an  automobile 
going  down  a  mountain  side,  if  the  brakes  should  fail  to 
work?  What  would  happen  to  an  automobile  in  the  traffic 
of  a  city,  if  it  had  no  brakes?  It  is  as  important  to  have  the 
brakes  in  good  working  order  as  to  have  the  engine  working 
well.  Brakes  do  their  work  by  increasing  friction. 

A  train  of  cars  weighs  many  hundreds  of  tons.  Because 
of  inertia,  a  large  amount  of  force  is  necessary  to  start  it. 
The  energy  is  supplied  by  the  burning  of  the  coal  or  oil  within 
the  engine,  but  the  energy  or  force  is  applied  between  the 
drive  wheels  and  the  track.  If  the  track  should  be  greased, 
what  would  happen?  How  is  friction  concerned  with  the 
starting  of  the  train  ? 

Again,  after  the  train  is  in  motion,  inertia  tends  to  keep 
it  in  motion :  on  a  level  track  the  engine  only  needing  to 
furnish  sufficient  force  to  overcome  the  friction  between  the 
wheels  and  the  track.  If  the  train  is  going  forty  miles  an 
hour,  it  will  be  seen  that  the  force  necessary  to  overcome 
its  inertia  will  be  very  great.  How  is  this  force  applied  to 
bring  it  to  a  stop?  Why  is  there  provision  for  sprinkling 
sand  on  the  rails?  Why  is  an  automobile  apt  to  skid  on 
a  wet  or  oily  pavement? 

Compare  walking  on  an  icy  pavement  with  walking  on 
a  pavement  having  no  ice.  Would  you  be  able  to  walk  if 
there  were  no  friction  between  your  feet  and  the  pave- 


MACHINES 


245 


ment?    Why  do  baseball  players  wear  spikes  on  their  shoes? 

In  bringing  a  vessel  alongside  a  dock,  a  rope  is  thrown 

out  and  wound  several  times  around  a  strong  post  (Figure 


FIGURE  185. 


a.  TIMBER     b.  SQUARE  OR  REEF 

c.  Two  HALF 

d.  BLACKWALL 

HITCH.                  KNOT. 

HITCHES. 

HITCH. 

The   commonest 

Useful  because 

Used  to  secure  a 

knot  for  tying  two 

they    are     easily 

rope  to  a  hook. 

ropes  together.  Fre- 

made    and     will 

quently  used  in  first 

not      slip     under 

aid  bandaging; 

any  strain. 

Neverslips  or  jams; 

easy  to  untie. 

185  a,  b,  c,  d).  .Suppose  the  rope  and  post  are  so  slippery 
that  there  is  no  friction,  what  will  happen?  What  keeps 
any  knot  from  slipping?  What  causes  threads  in  cloth  to 
remain  in  place  ? 

Lumber  is  fastened  together  by  nails  and  screws;  what 
prevents  them  from  dropping  out?  Endeavor  to  consider 
the  condition  of  things  if  friction  did  not  exist. 

Problem  11.  Causes  of  inefficiency  of  engines.  —  In 
engines  in  which  the  burning  of  fuel  is  the  source  of  energy, 
there  are  other  losses  in  addition  to  that  due  to  friction. 
Suggest  some  of  the  ways  in  which  energy  in  the  form  of 


246 


GENERAL  SCIENCE 


heat  is  lost  from  a  steam  engine;  also  the  gasoline  engine. 
It  has  been  estimated  that  in  the  steam  engine  about  95  per 
cent  of  the  energy  of  the  coal  is  lost,  and  that  the  efficiency  of 
the  engine  is  only  about  5  per  cent.  In  the  gasoline  engine, 
since  no  heat  escapes  in  the  ashes  and  smoke  and  less  surface 
is  exposed  to  be  cooled,  the  loss  is  considerably  less  and  the 
efficiency  of  the  engine  may  be  as  high  as  30  or  35  per  cent. 
In  the  oxidation  of  fuel  in  the  muscles  of  the  human  body, 
only  about  25  per  cent  of  the  energy  is  transformed  into 

working  energy ;  75  per  cent  of  it 
taking  the  form  of  heat.  Explain 
why  we  become  so  heated  while 
exercising.  Suggest  how  shivering, 
when  we  are  cold,  may  be  of  value 
to  the  body. 

Problem  12.  The  working  of 
the  gas  engine.  —  The  gas  engine 
has  become  of  great  importance 
not  only  because  of  its  economy 
of  fuel,  but  also  because  of  its  ease 
of  operation  and  lightness.  Its 
combination  of  great  power  with 

light  weight  has  made  possible  the 

FIGURE  186.— MOVEMENTS  OF 
PISTON  IN  A  FOUR-CYCLE  EN-  marvelous  development  of  the  air- 

GINE-  plane  and  automobile.  You  will 

be  interested  in  looking  into  the  working  of  the  gasoline 
engine  as  shown  in  the  motor  of  an  automobile. 

The  successive  positions  of  the  piston  may  be  seen  from 
the  examination  of  the  accompanying  diagrams. 

First  or  suction  stroke.  —  The  mixture  of  air  and  gasoline 
passes  into  the  cylinder.  Note  that  the  gasoline  is  not  a 
liquid  but  a  gas,  having  become  vaporized  in  the  carburetor. 


MACHINES  247 

Second  or  compression  stroke.  —  The  mixture  of  air  and 
gas  is  compressed. 

Third  or  power  stroke.  —  At  the  end  of  the  compression 
stroke,  the  air  and  gas  mixture  is  exploded  by  the  spark  that 
passes  between  the  two  wires,  and  the  piston  is  forced  down- 
ward. 

Fourth  or  exhaust  stroke.  —  The  piston  passes  back  into 
the  cylinder,  forcing  out  the  gases  which  remain  after  the 
explosion.  The  piston  is  now  in  position  for  the  beginning 
of  the  suction  stroke  again.  Note  the  position  of  the  intake 
and  exhaust  valves  at  each  stroke. 

Of  the  four  strokes  of  the  piston,  how  many  are  power 
strokes  ? 

As  four  strokes  are  necessary  to  complete  the  cycle  (circle), 
an  engine  of  this  kind  is  known  as  a  four-stroke  cycle  engine. 

The  power  developed  by  the  explosion  in  the  cylinder  is 
applied  to  moving  the  automobile  by  having  the  piston  rods 
connected  with  the  crank  shaft,  which  is  made  to  rotate  by 
the  up-and-down  stroke  of  the  piston  rod.  By  a  series  of 
cogs  called  gears,  the  power  is  applied  to  the  rear  axle,  caus- 
ing the  wheels  to  turn. 

Need  for  a  flywheel  —  What  causes  the  engine  to  run 
between  the  times  of  the  power  strokes?  A  one-cylinder 
engine  would  not  run  if  a  heavy  flywheel  were  not  at- 
tached to  a  continuation  of  the  crank  shaft.  The  power 
stroke  sets  in  motion  the  flywheel  which  by  its  rotation 
carries  the  crank  shaft  around  until  the  piston  is  in  position 
for  the  next  power  stroke. 

Advantage  of  a  number  of  cylinders.  —  The  first  automo- 
biles made  were  equipped  with  one-cylinder  gasoline  engines, 
but  now  they  are  fitted  with  engines  having  a  number  of 
cylinders;  four,  six,  eight,  twelve,  and  in  airplane  engines 


248 


GENERAL  SCIENCE 


MACHINES  249 

an  even  larger  number.  By  the  use  of  a  number  of  cylinders, 
the  power  is  more  continuously  applied,  withjthe  result  that 
the  engine  runs  much  more  steadily. 

Explain  how  a  four-cylinder,  four-cycle  engine  would  have 
four  times  as  many  power  strokes  as  a  one-cylinder  engine. 

How  the  spark  is  furnished.  —  When  an  engine  is  started, 
the  spark  is  usually  furnished  by  an  electric  current  generated 
by  a  battery.  However,  after  the  engine  has  started,  it 
generates  its  own  electricity  by  means  of  a  magneto.  This 
explains  how  an  automobile  may  be  started  without  the 
use  of  batteries  by  allowing  it  to  coast  downhill  or  by  turn- 
ing the  crank  rod  a  number  of  times,  sometimes  called 
"  spinning  on  the  magneto."  It  is  evident  that  the  mag- 
neto must  be  equipped  with  an  apparatus  for  timing  the 
spark,  for  if  the  explosion  occurs  a  fraction  of  a  second  too 
soon  or  too  late,  the  results  will  be  unsatisfactory. 

Explain  why  the  engine  must  be  started  by  hand  (by 
cranking)  or  by  a  self-starting  apparatus. 

Cooling  the  engine.  —  As  the  cylinders  become  very  hot 
during  the  explosions,  they  must  be  cooled.  This  is  usually 
done  by  surrounding  the  cylinders  with  a  space  filled  with 
water.  The  water  circulates  through  the  radiator  where 
it  is  cooled  by  air  drawn  through  the  meshes  of  the  radiator 
by  a  fan.  Some  automobiles  are  cooled  by  air  without  the 
assistance  of  water. 

As  all  parts  must  slide  easily  in  order  to  avoid  loss  of 
power  and  overheating  by  friction,  there  must  be  a  sys- 
tem by  which  the  engine  automatically  oils  itself. 


250  GENERAL   SCIENCE 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Plan  and  carry  out  a  series  of  demonstrations  to  illustrate  the 
various  uses  of  levers. 

2.  Construct  a  windlass  and  demonstrate  its  use  to  the  class. 

3.  Construct  a  set  of  cogwheels  by  which  power  is  gained  at  the 
expense  of  speed. 

.4.   Construct  a  set  of  cogwheels  by  which  speed  is  gained  at  the 
expense  of  power. 

5.  Demonstrate  the  use  of  cogs  in  several  machines.     Calculate 
the  kind  and  amount  of  advantage  gained. 

6.  Construct  a  toy  machine  in  which  belts  are  used. 

7.  Construct  several  sets  of  pulleys  and  demonstrate  their  use. 

8.  Construct  an  inclined  plane  and  show  its  value. 

9.  Work  o'ut  the  different  kinds  of  simple  machines  used  in  the 
construction  of  the  sewing  machine  or  other  machines  familiar  to  you. 

10.  Work  out  the  efficiency  of  a  number  of  machines. 

11.  Demonstrate  the  various  kinds  of  knots  described  in  the  Manual 
of  the  Boy  Scouts  of  America. 

12.  Make  a  simple  cylinder  with  piston  to  illustrate  the  action  of 
the  piston  of  an  automobile  cylinder. 

REPORTS 

1.  How  things  that  were  done  by  hand  a  hundred  years  ago  are 
now  performed  by  machines. 

2.  How  the  power  developed  by  the  automobile  engine  is  trans- 
mitted to  the  drive  wheels. 

REFERENCES  FOR  PROJECT  XXII 

1.  Great  Inventors  and  Their  Inventions,  Bachman.     American 
Book  Company. 

2.  Harper's  Machinery  Book  for  Boys,  Adams.     Harper  &  Bros. 

3.  Mechanics  of  Sewing  Machines.     Singer  Sewing  Machine  Com- 
pany. 

4.  Stories  of  Useful  Inventions,  S.  E.  Forman.    Century  Company. 

5.  The  Story  of  Agriculture  in  the  United  States,  Sanford.     D.  C. 
Heath  &  Co. 


MACHINES  251 

6.  The  Story  of  Iron  and  Steel,  Smith.     D.  Appleton  &  Co. 

7.  The  Romance  of  Modern  Mechanism,  Williams.     J.  B.  Lippin- 
cott  Company. 

8.  Stories   of   Inventors,    Doubleday.     Doubleday,    Page    &   Co. 
(Automobiles.) 

9.  The  Romance  of  Modern  Locomotion,  Williams.     J.  B.  Lip- 
pincott  Company. 

10.  Historic  Inventions,  Holland.     Geo.  W.  Jacobs,  Philadelphia. 

11.  The  Boy  Mechanics.     Chicago  Popular  Mechanics  Company. 


PROJECT  XXIII 
ELECTRICITY  AND   MODERN  LIFE 

IF  a  man  who  lived  a  century  ago  should  visit  us,  he  would 
be  much  surprised  at  the  many  changes  which  have  occurred 
since  his  tune.  Especially  would  he  be  amazed  at  those 
inventions  which  depend  upon  electrical  energy.  Elec- 
tricity was  being  studied  by  some  of  the  scientists  of  his 
time,  but  probably  none  of  them  had  the  faintest  idea  of  the 
practical  importance  that  it  would  have. 


FIGURE  188.  —  GRAND  CENTRAL  TERMINAL,  NEW  YORK  CITY,  BEFORE 
ELECTRIFICATION. 

The  first  electric  motor,  a  very  inefficient  one,  was  con- 
structed in  1838,  and  it  was  not  until  1871  that  really  efficient 
motors  and  dynamos  were  used.  Electric  lighting  on  a 
commercial  scale  was  used  for  the  first  time  in  Paris  and 
London  in  1877.  Think  of  the  many  things  which  this 
visitor  from  a  previous  century  would  see  for  the  first  time. 
Make  a  list  of  the  appliances  of  present  day  life  which  make 
use  of  electrical  energy. 

252 


ELECTRICITY  AND  MODERN  LIFE  253 

Problem  1.  How  the  electric  bell  rings.  —  One  of  the 
best  methods  of  beginning  the  study  of  the  way  in  which  we 
make  use  of  electrical  energy  is  by  an  examination  of  the 
electric  bell,  which  not  only  is  familiar  to  us  all,  but  il- 
lustrates many  rather  simple  things  concerning  electricity 
which  have  very  wide  application.  You  already  know  a 
number  of  facts  about  the  bell  and  the  conditions  necessary 
for  its  working. 


FIGURE    189.  —  GRAND   CENTRAL  TERMINAL,   NEW  YORK  CITY,  AFTER 
ELECTRIFICATION. 

How  is  the  bell  connected  with  the  place  from  which  it 
may  be  rung,  —  for  example,  the  front  door?  How  many 
wires  run  to  the  bell  ?  Are  the  metal  wires  bare  or  covered  ? 
Are  the  wires  covered  where  they  are  fastened  to  the  bell? 
Of  what  metal  are  the  wires  made  ?  To  ring  the  bell,  what 
must  you  do  to  the  push  button  ?  This  brings  together  the 
ends  of  the  two  wires  so  that  there  is  a  continuous  metal 
circuit  beginning  at  one  side  of  the  bell  and  ending  at  the 
other. 

Will  the  bell  ring  if  the  wire  is  broken  at  any  place? 
Most  of  you  know  that  the  wires  are  usually  connected  with 
one  or  more  batteries  which  in  some  way  generate  electricity, 
and  that  the  batteries  must  occasionally  be  renewed  or  re- 
placed by  fresh  ones.  If  you  have  removed  the  small  metal 


254 


GENERAL   SCIENCE 


covering  just  above  or  below  the  bell  itself,  you  have  noticed 
two  small  spools  of  wire  lying  side  by  side.  Each  is  made 
of  a  rod  of  iron,  around  which  is  wound  some  covered  copper 
wire. 

When  the  current  from  the  batteries  passes  through 
this  copper  wire,  it  magnetizes  (makes  a  magnet  of)  the 
rod  of  iron.  One  end  of  the  wire  is 
connected  with  one  of  the  binding 
posts.  At  one  end  of  the  spools  or 
coils  is  an  iron  bar  called  an  arma- 
ture held  in  position  by  a  spring, 
so  that  when  the  circuit  is  open 
(that  is,  when  the  push  button  is 
not  pressed  down  bringing  the  two 
ends  of  the  wire  into  contact)  it  does 
not  quite  touch  the  iron  centers  of 
the  spools. 

From  the  diagram  (Figure  190) 
note  the  course  taken  by  the  current 
of  electricity  in  passing  from  the  wire 
connected  with  one  binding  post  to 
the  wire  connected  with  the  other.  Note  also  that  the 
clapper  is  connected  with  the  armature.  When  the  circuit 
is  closed,  it  will  be  seen  that  the  coils  are  magnetized  and 
the  armature  is  drawn  toward  the  coils,  causing  the  clapper 
to.  strike  the  bell. 

The  pulling  of  the  armature  toward  the  coils  breaks  the 
circuit.  Immediately  the  coils  lose  their  power  to  at- 
tract the  armature,  which  springs  back  and  closes  the  cir- 
cuit. Again  the  coils  are  able  to  attract  the  armature,  and 
the  clapper  strikes  the  bell.  This  breaking  and  making 
of  the  circuit  continues  as  long  as  pressure  is  maintained 
on  the  push  button. 


FIGURE  190.  —  DIREC- 
TION OF  CURRENT TH-ROUGH 
AN  ELECTRIC  BELL. 


ELECTRICITY  AND  MODERN  LIFE 


255 


Problem  2.  How  magnets  are  used.  —  The  current  of 
electricity  passing  through  the  coil  of  wire  gives  the  iron 
rod  around  which  it  is  wound  the  power  of  a  magnet.  This 
kind  of  magnet  is  tem- 
porary, possessing  its 
power  only  when  the 
current  of  electricity  is 
passing  through  the 
wires.  For  this  reason 
it  is  called  an  electro- 
magnet (Figure  191). 
Electromagnets  are  used  FlGURE  ' 

in  many  electrical  devices  (Figure  192) ;    among  which  are 
telephone,  telegraph,  and  wireless  apparatus,  ignition  sys- 


FIGURE  192.  —  DYNAMO  ATTACHED  TO  AN  AMBULANCE. 

The  current  generated  by  the  dynamo  produces  an  electro-magnet 

which  is  used  to  remove  pieces  of  metal  from  eyes. 


256 


GENERAL  SCIENCE 


tern  of  automobiles,  and  in  electric  motors  and  dynamos. 
Large    electro-magnets    attached  to  cranes    are   used    to 


^v^jHMSli 


FIGURE  193. — ARRANGEMENT  OF  IRON  FILINGS  BETWEEN  POLES  OF  A  MAGNET. 

lift  masses  of  iron  which  may  be  dropped  at  the  desired 
spot  by  simply  breaking  the  circuit. 

The  action  of  permanent  magnets  may  be  observed  by 
experimenting  with  a  common  horseshoe  or  bar  magnet. 

Experiment.  —  Place  the  magnet  under  a  piece  of  paper  over  which 
iron  filings  have  been  scattered.  Gently  tap  the  paper  and  observe 
the  position  taken  by  the  filings  (Figure  193). 

Experiment.  —  Rub  a  needle  along  the  magnet  and  move  it  near 
some  fine  iron  filings.  What  has  happened  to  the  needle?  Suspend 
the  needle  horizontally  by  an  untwisted  silk  thread.  Move  one  end 
(pole)  of  the  magnet  near  one  end  of  the  needle.  Reverse  the  magnet 
and  approach  the  same  end  of  the  needle  with  the  other  pole  of  the 
magnet.  What  is  the  result  ?  Allow  the  needle  to  remain  suspended 


ELECTRICITY  AND  MODERN  LIFE 


257 


undisturbed.  What  position  does  it  take  ?  The  earth  itself  is  a  great 
magnet ;  one  magnetic  pole  being  near  the  geographic  north  pole,  and 
the  other  near  the  geographic  south  pole.  A  magnetic  needle,  therefore, 
which  swings  freely  will  take  an  ap- 
proximate north  and  south  position 
(Figure  194).  What  practical  use  is 
made  of  this  fact?  The  use  of  the 
compass  has  had  a  great  influence 
upon  the  development  of  navigation,  - 

Problem   3.    How   chemical    |j| 
energy  may  be  changed  into    • 
electrical    energy.  —  The  elec- 
trical    energy     which     caused 

,i          .      .  .    ,,       ,    „  FIGURE  194.  — MAGNETIC  NEEDLE. 

the    ringing    of   the    bell    was 

generated   in  a  battery   cell  by    a  chemical  action.    The 


FIGURE   195.  —  FIRST  OF  ALL    ELECTRIC    BATTERIES   PREPARED  BY  VOLTA, 

A.D.   1800. 

At  the  right  is  the  famous  Voltaic  pile,  consisting  of  a  series  of  alternate 
disks  of  zinc  and  copper  separated  by  moistened  felt.  At  the  left  each 
cell  consists  of  a  plate  of  copper  and  one  of  zinc  immersed  in  brine. 

simplest  form  of  a  cell  of  this  kind,  called  the  voltaic  cell, 
was  invented  in  1800  by  Alessandro  Volta,  a  professor  in 


258  GENERAL  SCIENCE 

an  Italian  University  (Figure  195).     You  can  easily  make 
a  cell  of  this  kind. 

Experiment.  —  In  a  jar  containing  dilute  sulphuric  acid  place  two 
metal  plates ;  one  of  zinc  and  the  other  of  copper.  If  each  plate  (called 
an  electrode)  is  connected  by  means  of  a  wire  with  the  binding  posts  of 
an  electric  bell,  the  bell  will  ring.  After  a  few  minutes  the  bell  ceases 
to  ring  although  the  circuit  has  not  been  broken. 

An  examination  of  the  copper  plate  will  show  that  it  is 
covered  with  bubbles  of  a  gas,  so  that  the  acid  is  not  able  to 
touch  it.     The  battery  is  now  said  to  be  polarized.     If  the 
bubbles  are  rubbed  off,  the  bell  will  again  begin  to  ring. 
Various   methods   have  been  used  to 
prevent  this  polarization.   One  method 
is  illustrated  by  the  gravity  cells.     In 
this  cell,  the  copper   is  placed  at  the 
bottom  of  the  jar  in  a    solution    of 
copper    sulphate,  (blue  vitriol) ;    and 
the  zinc  near  the  top   in   weak    sul- 
phuric  acid.     The   blue  vitriol   solu- 
tion  is   heavier   than    the   acid,   and 
remains    at   the    bottom;    hence  the 
FlGURE  CEuT01^1^     Imme'     gravity     cell     (Figure     196). 

A  solution^!  zinc  sul-   The    blue    vitrio1    Or    COPP6r     suIPhate 

phate.  B,  solution  of  solution  prevents  the  gas  (hydrogen) 
'  from  Caching  the  copper  plate,  but 
it  causes  copper  to  separate  from 
the  solution  and  be  deposited  on  the  copper  plate  as  a 
bright  layer. 

In  the  Daniell  cell,  the  zinc  and  sulphuric  acid  are  in  a 
porous  cup  which  is  placed  in  a  jar  containing  the  copper 
and  blue  vitriol  solution  (Figure  197).  In  another  form  of 
cell,  one  electrode  is  carbon  and  the  other  zinc,  and  the 


ELECTRICITY  AND  MODERN  LIFE 


259 


FIGURE   197.  — DANIELL 
CELL. 


liquid  in  which  they  are  immersed  is  a  strong  solution  of 

sal  ammoniac  (ammonium  chloride). 

The  dry  cell,  which  for  most  pur- 
poses  is  more   convenient   than   any 

other,  is  like  the  last  cell  mentioned, 

except  that,  instead  of  a  jar,  a  cup  or 

cylinder  made  of  zinc  is  used  as  the 

container,  and  this  forms  one  electrode 

(Figure    198).     Then   instead   of    sal 

ammoniac  solution  being  used,  a  moist 

paste  saturated  with  sal  ammoniac  and 

usually  containing  manganese  dioxide 

to  prevent  polarization,  is  packed  be- 
tween the  carbon  and  this  zinc  outer 

wall. 
Problem  4.    How  electricity  is  measured :  volts,  amperes, 

kilowatts.  —  In  all  the  cells  discussed,  you  have  noticed  that 

there  has  been  greater  chemical  action  at  the  zinc  electrode 

than  at  the  other.  This  gives  rise 
to  what  may  be  called  an  electri- 
cal pressure  or  electromotive  force 
(E.  M.  F.)  and  causes  a  current 
somewhat  as  differences  in  water 
pressure  will  produce  a  current. 
This  current  passes  from  the  zinc 
to  the  other  electrode  within  the 
cell,  and  from  the  carbon  to  the 
zinc  electrode  through  the  wire 
circuit. 

The  unit  of  electromotive  force 
is  called  the  volt.     It  is  approxi- 
FIGURE  198.— DRY  CELL,      mately  the  electromotive  force  of 


260  GENERAL   SCIENCE 

the  simple  voltaic  cell.  By  connecting  the  several  cells  in 
series,  that  is,  by  connecting  the  carbon  of  one  cell  with 
the  zinc  electrode  of  the  next  one,  etc.,  the  voltage  or  elec- 
tromotive force  of  the  battery  of  cells  will  be  equal  to  the 
sum  of  the  electromotive  forces  of  the  individual  cells. 
The  electrical  pressure  is  measured  by  an  instrument  called 
the  voltmeter. 

The  pressure  in  a  water  pipe  may  be  very  great,  but  yet 
there  may  be  very  little,  if  any,  flow  of  water  because 
the  faucet  opening  is  quite  small.  On  the  other  hand,  the 
pressure  may  be  relatively  low  with  a  large  flow,  providing 
there  is  nothing  to  obstruct  the  current.  In  the  same  way, 
the  amount  of  electricity  that  passes  through  a  wire  de- 
pends upon  the  voltage  or  pressure,  and  upon  the  resistance. 
The  unit  of  resistance  is  called  an  ohm,  in  honor  of  Georg 
Ohm,  an  investigator  in  electricity,  who  worked  during  the 
early  part  of  the  nineteenth  century. 

The  unit  of  current  is  called  an  ampere,  in  honor  of  another 
great  scientist  who  was  contemporary  with  Volta  and  Ohm. 
The  relation  of  current,  electromotive  force,  and  resistance 
to  flow  is  expressed  in  Ohm's  law : 

electromotive  force  Volts         ~, 

Current  = : or  Amperes  =  ™ or  Ohms  = 

resistance  Ohms 

Volts 


Amperes 

The  instrument  used  to  measure  the  current  is  called  an 
ammeter.  A  rheostat  is  a  device  by  which  the  amount  of 
resistance  may  be  controlled.  Just  as  the  amount  of  work 
done  by  water  power  depends  upon  the  pressure  and  the 
amount  of  water,  so  the  work  done  by  an  electric  current 
may  be  determined  by  multiplying  the  voltage  (pressure) 
by  the  amperage  (amount  of  electricity). 


ELECTRICITY  AND  MODERN  LIFE 


261 


The  unit  of  work,'  called  a  watt  in  honor  of  James  Watt, 
is  the  work  done  by  one  ampere  having  the  voltage  of  1. 
Since  this  is  such  a  small  unit,  the  kilowatt,  which  is  equal 
to  1000  watts,  is  more  often  used.  Electrical  energy  is 
charged  for  by  the  kilowatt  hour,  which  is  the  energy  fur- 
nished by  a  current  providing  in  one  hour  one  kilowatt  of 
work.  A  kilowatt  hour  is  equal  to  about  Ij  horsepower 
(hours),  and  in  New  York  City  costs  from  4|  to  7  cents. 


FIGURE  199.  —  STRUCTURE  OF  AN  INDUCTION  COIL. 
P,  P,  primary  wire  connected  with  battery.  5,  S,  ends  of  sec- 
ondary coil  between  which  sparks  leap.  F,  iron  block  which  is 
pulled  back  when  iron  core  is  magnetized,  thus  breaking  the  cir- 
cuit. The  iron  core  is  then  demagnetized  and  the  spring  h  pulls 
back  the  iron  block  F  closing  the  circuit  again.  Note  that  there 
are  more  turns  of  the  secondary  than  of  the  primary. 

Problem  5.  Use  of  induction  coil  in  wireless  telegraphy 
and  in  the  production  of  spark  in  gasoline  engine. — By 
means  of  a  spark  coil,  a  sufficiently  high  voltage  is  produced 
to  cause  the  current  to  leap  across  an  air  space,  forming  a 
spark.  It  consists  of  a  central  iron  core,  surrounded  by  a 
coil  of  heavy  wire  called  the  primary,  and  by  a  second  outside 
coil,  the  secondary  (Figure  199).  The  primary  is  connected 
with  a  few  cells  of  a  battery,  and  with  an  interrupter  as  in 
the  case  of  the  electric  bell. 


262 


GENERAL   SCIENCE 


It  is  by  the  use  of  the  induction  coil  that  the  sparks  are 
produced  which  explode  the  gasoline  vapor  in  the  cylinders 
of  a  gasoline  engine,  and  which  send  out  the  electric  waves 
of  the  wireless  telegraph.  An  Induction  coil  is  also  an 
essential  part  of  the  transmitting  apparatus  of  a  long  dis- 
tance telephone. 

In  the  wireless  telegraph,  the  electric  waves  act  upon  the 
antenna,  which  is  made  of  a  number  of  parallel  wires  sus- 
pended on  insulating  supports  from  a  mast  or  tower,  and  con- 
nected by  a  single  wire  with  a  rod  on  one  side  of  the  spark 


FIGURE  200.  —  U.  S.  ARMY  WIRELESS  OPERATORS  RECEIVING  MESSAGES 
FROM  AN  AIRPLANE,  TOURS,  FRANCE. 

gap.  Electric  waves  pass  out  into  surrounding  space  from 
the  antenna  and  cause  similar  electric  waves  in  the  antenna 
of  the  receiving  station,  which  by  means  of  pieces  of  ap- 
paratus called  crystal  detectors  or  audion  detectors,  are 
made  susceptible  of  being  detected  by  a  telephone  receiver. 

Problem  6.    How  mechanical  energy  is  changed  into 
electrical   energy  by  the   dynamo.  —  In  our  discussion  of 


ELECTRICITY  AND  MODERN  LIFE 


263 


oxidation  of  fuel,  the  use  of  water  power,  etc.,  we  under- 
stood that  heat  energy  and  mechanical  energy  may  be  trans- 
formed into  electrical  energy.  This  is  done  by  the  dynamo, 
a  machine  complicated  in 
appearance,  which,  how- 
ever, in  its  simplest  form 
is  not  difficult  to  under- 
stand. 

You  will  it  call  that  in 

the  electric  bell  a  current        FiouRE.20i.-A  SIMPLE  DYNAMO 
of        electricity        passing        N,  north  pole  of  a  permanent  magnet. 
through  the  coil  of  wire,    5'  south  P°le  of  a  Perm*nent  magnet. 

.  .  ,    G,  point  of  contact  of  brushes  for  carrying 

wound  around  a  piece  of   current  into  outside  circuit. 
iron,  caused  the   iron   to 

become  a  magnet.  In  generating  a  current  of  electricity 
by  a  dynamo,  the  reverse  occurs.  If  a  coil  of  wire  is 
rotated  continuously  between  the  poles  of  a  strong  mag- 
net, an  electric  current  is  produced  in  the  coil  of  wire 
(Figure  201).  The  effect  of  a  magnet  in  producing  an 

electric   current   in  a 
coil  of   wire  may  be 
shown  by  the  follow- 
ing experiment- 
Experiment.  —  Move  a 
magnet  in  and  out  of  a 
coil  of  wire,  the  ends  of 
which   are  attached  to  a 
FIGURE  202.  —  PRINCIPLE  OF  DYNAMO. 


Current  produced  by  thrusting  magnet  into  a 
coil  of  wire. 


galvanometer  (an  instru- 
ment for  detecting  cur- 
rents of  electricity  (Figure 
202) .  It  will  be  noted  that 

trie  current  is  produced  only  when  the  magnet  is  in  motion,  and  that 
the  direction  of  the  current  is  in  one  direction  when  the  magnet  is 
pushed  into  the  coil,  and  in  the  opposite  direction  when  it  is  pulled  out. 


264 


GENERAL   SCIENCE 


The  essential  parts  of  a  dynamo  are  (1)  a  rotary  coil 
(armature),  (2)  a  stationary  magnet  (field  magnet),  and 
(3)  a  sliding  contact  device  for  carrying  the  current  from 
the  armature  to  the  external  circuit.  The  efficiency  of  the 

dynamo  is  increased  by  the 
use  of  electro-magnets  as  field 
magnets.  Large  dynamos 
may  develop  electrical  power 
equal  to  8000  or  10,000 
horse  power.  For  some  pur- 
poses an  alternating  current 


FIGURE    203.  —  A    SIMPLE    COM- 
MUTATOR. 

a  and  b,  two  halves  of  a  split  tube  is  satisfactory,  but  for  other 
connected  with  the  two  ends  of  the 
coil  of  the  armature.  +  and  — , 
two  brushes  connected  with  the  ex- 
ternal circuit  L,  L.  S,  shaft  upon 
which  a  and  b  are  mounted. 


purposes 
rent     in 


a  continuous  cur- 
one  direction  is 
necessary.  By  means  of  an 
attachment  called  a  commu- 
tator (Figure  203),  the  alternating  current  of  the  dynamo 
may  be  changed  to  a  direct  current. 


FIGURE  204.  —  USE  OF  ELECTRIC  MOTOR  IN  RUNNING  SEWING  MACHINE. 


ELECTRICITY  AND  MODERN  LIFE 


265 


Problem  7.  How  electrical  energy  is  changed  into  me- 
chanical energy  by  the  electric  motor.  —  A  motor  (Figure 
204)  by  which  the  electrical  energy  developed  by  the  dy- 
namo is  changed  back  into  mechanical  energy  is  really  the 
reverse  of  a  dynamo ;  a  current  passes  both  into  the  field 
magnets  and  the  armature,  resulting  in  a  rotation  of  the 
armature,  which  by  means  of  belts,  etc.,  may  set  machinery 
in  motion.  The  principle  of  the  motor  may  be  illustrated 
in  the  following  way. 

Experiment.  —  Suspend  a  loop  or  a  coil  of  wire  between  the  poles 
of  a  magnet.  It  will  hang  in  any  position  in  which  it  is  placed.  If 
now  a  current  of  electricity  is  passed  through  it,  the  coil,  as  in  the 
case  of  the  electric  bell  coil,  becomes  a  magnet  and  takes  a  definite 
position  with  reference  to  the  field  magnets.  If  the  current  is  re- 
versed, the  coil  swings  around  180°. 


FIGURE  205.  —  EXPERIMENTAL  ILLUSTRATION  OF  PRINCIPLE  OF  THE  MOTOR. 

The  dotted  line  represents  the  position  of  the  wire  as  current  passes 
through  it. 

Figure  205  represents  the  influence  of  a  magnet  upon  a 
wire  through  which  a  current  of  electricity  is  passing. 
It  can  easily  be  understood  how  the  armature  will  con- 


266 


GENERAL   SCIENCE 


tinue  its  rotation,  if  the  current  is  reversed  at  proper  in- 
tervals of  time. 

Problem  8.  How  electroplating  and  electrotyping  are 
done.  —  It  will  be  recalled  that  in  the  gravity  cell,  in  which 
there  was  a  solution  of  copper  sulphate,  a  layer  of  copper 
was  deposited  on  the  copper  electrode.  By  this  process 
the  electrode  was  really  copper-plated.  Copper-plate  some 
object  such  as  a  piece  of  tin  or  nickel  as  follows. 

Experiment.  —  Suspend  in  a  jar  of  copper  sulphate  the  object  to 
be  plated,  and  a  piece  of  copper;  connect  the  former  with  the  nega- 
tive and  the  latter  with  the  positive  terminal  (pole)  of  a  battery. 

Silver,  gold,  or  nickel  plating  may  be  done  in  a  similar 
way.  Name  various  objects  which  have  been  plated  with  a 

metal.      In  each   case,   state   the 
reason  for  doing  so. 

Electrotyping.  —  This  power  of 
the  electric  current  to  cause  a 
layer  of  metal  to  be  formed  on 
an  object  is  made  use  of  in 
printing.  This  book  and  nearly 
all  others  are  printed  from  elec- 

FIGURE  206.  — SILVER  PLATING,  trotype  plates.  The  type  is  set 
•.solution of  up  and  a  mold  of  it  is  taken  in 
wax.  The  type  may  now  be 
taken  down  and  used  again.  The 
mold  is  coated  with  graphite  (a  form  of  carbon)  to  make 
it  a  conductor,  and  is  immersed  in  a  bath  of  copper  sul- 
phate, in  which  is  suspended  a  piece  of  pure  copper. 

A  current  of  electricity  is  now  sent  through  the  liquid 
from  the  copper  to  the  graphite-covered  wax  plate  and  in  this 
way  a  layer  of  copper  is  deposited  on  the  wax  plate.  The 


a,  bar  of  silver, 
a  silver  compound,     c,  objects 
to  be  plated. 


ELECTRICITY  AND  MODERN  LIFE 


267 


wax  is  replaced  then  by  metal  to  give  strength  to  the  mold. 
This  electrotype  plate,  which  is  an  exact  reproduction  of  the 
original  page  of  type,  may  be  conveniently  used  to  print 
thousands  of  copies,  whereas  the  type  is  awkward  to  handle 
and  soon  wears  down. 

In  the  printing  of 
newspapers  a  much 
quicker  method  is 
necessary.  A  ma- 
chine called  the  lino- 
type is  used.  The 
operator,  by  manip- 
ulating the  keys  of 
a  keyboard  very 
much  as  in  using  the 
typewriter,  sets  the 
type.  The  type  is 
then  pressed  against 
melted  metal,  and  an 
imprint  made  which 
is  used  in  printing 
the  paper. 

The  electric  current 
may  also  be  used  in 
refining  metals ;  those 

refined     in     this   way  FIGURE  207. -AN  ELECTROTYPE. 

being  the  purest  ob-  Photograph  of  the  plate  from  which  a  page 
tainable.  of  a  book  is  printed. 

Problem  9.  How  heat  is  produced  by  electricity.  — 
Name  various  household  appliances  in  which  heat  is  pro- 
duced by  an  electric  current.  The  way  in  which  this  is 
done  is  illustrated  as  follows. 


268 


GENERAL   SCIENCE 


Experiment.  —  Make  a  circuit  of  several  electric  cells  and  a  copper 
wire  of  the  thickness  generally  used  in  making  connections.  Now 
replace  a  small  portion  of  the  copper  wire  with  fine  iron  or  German 
silver  wire  wound  around  the  bulb  of  a  thermometer.  What  is  the 
result  ? 

The  resistance  of  small  wires  to  the  current  of  electricity 
is  much  greater  than  the  resistance  of  large  wires,  and  the 
electrical  energy  is  changed  into  heat  energy.  This  is 

similar  to  the  way  that 
mechanical  energy  when 
resisted  by  friction  is 
changed  into  heat  energy. 
All  the  electric  appliances 
you  have  named,  such  as 
flatirons,  toasters,  curling- 
iron  heaters,  electric  chaf- 
ing dishes,  electric  stoves, 
foot  warmers,  car  heaters, 
bacteriological  incubators 
and  sterilizers,  are  heated 
in  this  way  (Figure  208). 

Industrially,  the  changing  of  electrical  energy  into  heat 
energy  has  made  possible  many  important  processes.  An 
intense  heat  (about  3000°  C.)  is  developed  in  the  electric 
furnace,  due  to  resistance  offered  to  the  passage  of  the  cur- 
rent. Some  of  the  uses  to  which  the  electric  furnace  has 
been  put,  because  of  the  intense  heat  generated,  are  the  pro- 
duction of  carborundum,  the  most  important  abrasive  used ; 
artificial  graphite,  used  in  the  manufacture  of  electrodes 
and  lubricants ;  and  smelting,  the  refining  of  metals. 

Problem  10.  How  electric  lights  are  produced.  —  Ob- 
servation of  an  incandescent  electric  light  lamp  will  show 


FIGURE  208.  —  ELECTRIC  FLATIRON. 

E,  wires  offering  great  resistance  to 
electric  current.     A,  wooden  handle. 


ELECTRICITY  AND   MODERN  LIFE 


269 


that  there  is  within  the  bulb  a  very  slender  filament,  which 
becomes  white-hot  when  the  current  is  turned  on.  Evi- 
dently the  condition  here  is  similar  to 
that  which  we  observed  in  obtaining 
heat  from  the  electric  current.  Would 
you  consider  the  resistance  to  the  cur- 
rent to  be  greater  or  less  in  the  lamp 
than  in  the  wire  of  a  heating  device? 
The  wires  in  an  electric  stove  would  meltj 
or  become  oxidized  if  raised  to  such  a  FIGURE  209.— CARBON 
high  temperature.  What,  therefore,  do  FlLAMENT  LAMP- 
you  consider  must  have  been  the  great  problem  in 
the  development  of  the  incandescent  lamp? 
The  bulb  contains  no  air.  What  is  the 
advantage  of  this  ?  Very  few  substances 
have  been  found  capable  of  carrying  the 
current  and  yet  able  to  remain  in  a  solid 
form  at  the  temperature  necessary  for  the 
production  of  light.  For  many  years  spe- 
cially treated  carbon  filaments  were  used  (Fig- 
FIGURE  210.—  ure  209).  More  recently,  metallic  filaments 
have  very  largely  replaced  the  carbon  ones; 
the  most  satisfactory  filament  being  made 
of  tungsten  (Figure  210).  It  uses  only  about  one  third  as 
much  .electricity  as  the 
carbon  to  produce  the 
same  amount  of  light 
(Figure  211). 

The  name  which   has    FIGURE  211.— AMOUNT  OF  LIGHT  GIVEN 
.  ,       j  BY  DIFFERENT  INCANDESCENT  LAMPS. 

been    the    most    closely 

.  i       |T      .  The  length  of  the  arrows  represents  the 

associated   With   the   im-  intensity   Of    light  given  off  •  in    different 
provement  of  the  incan-  directions. 


TUNGSTEN  FILA- 
MENT LAMP. 


Gem  lamp 


Tungsten  Lamp 


Carbon  Lamp 


270  GENERAL   SCIENCE 

descent  lamp,  as  well  as  with  almost  every   improvement 
in  the  application  of  electricity,  is  Thomas  A.  Edison. 

The  voltage  of  the  electricity  in  the  main  distributing 
wires  is  very  high.  You  will  find,  however,  that  the  electric 
light  bulbs  in  your  house  are  probably  labeled  110  volts. 
A  current  of  much  higher  voltage  is  dangerous  to  human 
life.  You  have  probably  noticed  on  some  electric  light  poles 
iron  boxes  from  which  wires  pass  to  the  neighboring  houses. 
These  boxes  are  called  transformers,  and  in  them  the  voltage 
is  changed  from  1100  or  2200  volts  to  110  volts.  Some- 
times transformers  are  used  in  the  house  to  still  further  re- 
duce the  voltage  of  a  current  used  for  ringing  electric  bells, 
running  electric  toys,  etc. 

To    prevent    danger    from    fire,    the    wires 
used  in  a  house  must  be  of  sufficiently  large 
size  to  carry  the  current  without   being   ap- 
preciably heated,  and  they  must  be  inclosed 
FIGURE  212.—    in  metal  conduits  or  tubes  in  walls  and  par- 

FusE>          titions.. 

An  amount  of  electricity  which  might  prove  harmful  is  pre- 
vented from  passing  into  a  wire  by  means  •  of  fuses  (Figure 
212),  which  are  pieces  of  metal 
of  a  low  melting  point  inserted 
in  the  circuit.  When  the  cur- 
rent becomes  too  strong  the 
fuse  melts  and  automatically 
breaks  the  circuit.  Wires  must 
all  be  carefully .  insulated  ;  that 
is,  covered  with  a  material 
which  will  not  conduct  an  elec- 
tric current.  FIGURE  2 13— POSITION  OF  CAR- 
The  arc  light,  which  is  of  very  SONS  IN  AN  ARC  LIGHT. 


ELECTRICITY  AND  MODERN  LIFE  271 

high  candle-power,  may  be  understood  from  a  demonstration 
of  the  lamps  of  a  projection  lantern.  It  will  be  noted  that 
there  are  two  carbons  (Figure  213),  which  are  first  brought 
into  contact  to  complete  the  circuit.  When  they  are  pulled 
apart,  the  circuit  is  not  broken  but  the  current  continues 
to  flow  across  the  space,  producing  the  arc.  The  (+) 
carbon  becomes  hollowed  out,  and  the  (  — )  carbon  be- 
comes pointed,  apparently  by  the  addition  of  particles 
of  carbon  to  it.  It  seems  quite  clear  that  particles  of 
carbon  jump  across  the  gap  between  the  two  carbons. 

Problem  11.  How  the  "  storage  battery "  is  used.  — 
Storage  batteries  have  come  into  common  use.  Most  of 
you  will  know  of  some  instances  of  their  use.  Find  out 
as  many  examples  as  you  can  of  the  use  of  storage  bat- 
teries. The  following  experiment  will  help  you  to  under- 
stand a  storage  battery. 

Experiment.  —  Suspend  two  pieces  of  lead  in  a  very  dilute  (1-40)  so- 
lution of  sulphuric  acid  in  a  battery  jar.  Connect  the  lead  plates  with 
a  battery  of  three  or  more  dry  cells.  Do  you  notice  signs  of  any  ac- 
tivity in  the  battery  jar  ?  After  allowing  current  to  pass  through  the 
lead  plates  for  about  five  minutes,  disconnect  the  dry  cells. 

Connect  the  wires  attached  to  the  lead  plates  to  an  electric  bell. 
Result? 

From  the  facts  that  one  of  the  plates  became  brown  and 
gas  is  given  off  from  the  plates  during  the  process  of  charg- 
ing, what  kind  of  a  change  do  you  think  is  taking  place? 
The  electric  current  in  passing  through  the  lead  plates  and  the 
sulphuric  acid  causes  changes  somewhat  like  the  ones  we 
observed  in  electroplating.  The  effect  is  to  make  these 
plates  unlike  each  other  in  a  way  similar  to  that  in  which 
the  zinc  plate  is  unlike  the  copper  plate  in  the  simple  voltaic 
cell.  When  the  two  changed  lead  plates  are  connected 


272 


GENERAL   SCIENCE 


with  an  electric  bell,  the  bell  rings,  showing  that  the  chemi- 
cal energy  which  has  been  derived  from  electrical  energy 
has  now  been  changed  back  again  into  electrical  energy. 

About  75  per  cent  of  the  electrical  energy  passed  into 
a  storage  cell  may  be  recovered  again  as  electrical  energy. 


FILLING  PLUG 
,  VALVE     : 


ELECTROLYTE: 

C  E  LL  Co  N  N  tQTO  R 

SCALING  NUT 
POST  GASKET 
NEGATIVE  POST 
NEGATIVE  STRAP 


WOOD  SEPARATOR 

POSITIVE  PLATE 

NEGATIVE  Pi-ATE 
RuBBERiJAR 

WOOD  CASE 


FIGURE  214.  —  STORAGE  BATTERY  DISSECTED  TO  SHOW  CONSTRUCTION. 

Heat  developed  during  the  process  of  charging  and  dis- 
charging the  cell  accounts  for  the  loss. 

Lighter  storage  cells  have  nickel  and  iron  plates,  but  the 
principle  of  their  action  is  the  same.  Electrical  energy  is 
changed  into  chemical  energy  which  is  changed  in  turn  again 
into  electrical  energy  when  the  cell  is  discharged.  Com- 
mercial storage  cells  are  made  of  a  large  number  of  plates 


ELECTRICITY  AND  MODERN  LIFE  273 

(Figure  214).  All  the  negative  plates  are  connected  with 
one  wire  and  all  the  positive  plates  with  another  wire. 
While  the  voltage  remains  the  same,  with  the  increased 
surface  of  plates  the  amperage  is  increased. 

Problem  12.  How  lightning  is  produced.  —  Lightning 
is  an  instantaneous  discharge  of  electricity  of  high  voltage 
between  a  cloud  and  some  object  on  the  earth  or  between 
two  clouds.  If  on  a  cold  day  you  scuffle  over  the  carpet  and 
then  hold  your  knuckle  to  the  gas  fixture  or  even  to  the 
cheek  of  another  person,  a  spark  will  be  produced.  Because 
of  friction  between  your  feet  and  the  carpet,  electricity 
called  static  electricity  has  been  generated.  Since  cold, 
dry  air  is  a  poor  conductor,  the  electricity  remains  upon 
your  body.  When,  however,  your  hand  is  brought  so  near 
the  gas  fixture  that  the  voltage  of  the  electricity  is  sufficient 
to  cause  it  to  leap  through  the  dry  air,  the  spark  results. 

In  the  formation  of  a  storm  cloud,  large  quantities  of 
static  electricity  are  generated  and  condensed  on  the  drops 
of  moisture.  When  the  voltage  becomes  sufficiently  great, 
the  electricity  is  discharged  to  the  earth  or  to  a  neighboring 
cloud.  Benjamin  Franklin's  experiment  in  which  he  drew 
lightning  from  the  clouds  is  a  very  interesting  one.  He 
flew  a  kite  into  the  thunderclouds,  using  a  string  which  was 
a  fair  conductor  of  electricity,  to  which  .was  attached  at  its 
lower  end  a  metal  key.  Near  the  lower  end  of  this  string 
was  a  silk  cord  (a  very  poor  conductor)  which  he  held  in  his 
hand.  Sparks  passed  between  the  key  and  the  ground. 

The  crackling  of  the  fur  of  a  cat  when  stroked,  and  of 
hair  when  combed  with  a  rubber  comb,  especially  on  a 
clear  cold  day;  and  the  tendency  of  tissue  paper,  when 
rubbed,  to  stick  to  the  wall,  are  common  examples  of  the 
manifestations  of  static  electricity  resulting  from  friction. 


274  GENERAL   SCIENCE 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Construct  an  electro-magnet. 

2.  Construct  electric  cells  of  various  kinds. 

3.  Construct  a  copper- or  nickel-plating  apparatus  and  plate  a 
number  of  objects. 

4.  Endeavor  to  rejuvenate  a  dry  electric  cell. 

5.  Use  of  ammeter  and  voltmeter  in  an  automobile. 

6.  Construct  an  induction  coil. 

7.  Make  a  model  showing  how  a  dynamo  works. 

8.  Make  a  model  showing  action  of  ah  electric  motor. 

9.  Construct  a  simple  electric  heater. 

10.   Calculate  the  cost  per  hour  of  the  different  electric  lights  in 
your  home  or  in  your  father's  store. 

REPORTS 

1.  The  story  of  the  discovery  and  development  of  the  electric 
light. 

2.  Give  a  sketch  of  the  life  of  Thomas  A.  Edison. 

3.  Benjamin  Franklin  and  electricity. 

4.  The  making  of  electroplates  from  which  books  are  printed. 

5.  The  printing  of  a  newspaper. 

REFERENCES  FOR  PROJECT  XXIII 

1.  Farmers'  Electrical   Handbook.     Western  Electric   Company, 
New  York,  50  cents. 

2.  The  Compass,  the  Signpost  of  the  World.     P.  R.  Jameson. 
Taylor  Instrument  Company,  Rochester,  N.  Y. 

3.  Benjamin  Franklin,  P.  E.  More.     Houghton  Mifflin  Company. 

4.  Great  Inventors  and  Their  Inventions.     Bachman.     American 
Book  Company.     (Edison.) 

5.  Modern  Triumphs,  E.  M.  Tappan,  Editor.     Houghton  Mifflin 
Company.     (Edison  and  Electric  Light.) 

6.  Wonders  of  Science.     Houghton  Mifflin  Company.    (An  Inter- 
view with  Edison.) 

7.  Electricity  and  Its  Everyday  Uses,  J.  F.  Woodhull,    Double- 
day,  Page  &  Co. 


ELECTRICITY  AND  MODERN  LIFE  275 

8.  The  Story  of  Great  Inventions,  E.  E.  Burns.     Harper  &  Bros. 
(Electric  Furnace.) 

9.  The  Book  of  Wireless,  A.  F.  Collins.     D.  Appleton  &  Co.     (Tele- 
graph, Telephone.) 

10.  Book  of  Electricity,  A.  F.  Collins.     D.  Appleton  &  Co. 

11.  Harper's  Everyday  Electricity,  Shafer.     Harper  &  Bros. 

12.  Wonders  of  Science,  Houghton  Mifflin  Company.     (The  Mak- 
ing of  a  Book.) 

13.  Great  Inventions  and  Discoveries,  Piercy.     Chas.  E.  Merrill 
Company.     (Telegraph.) 

14.  Stories   of   Inventors,   Doubleday.     Doubleday,   Page   &   Co. 
(Telephone.) 

15.  The  Boy's  Life  of  Edison,  Meadowcraft.     Harper  &  Bros. 

16.  Boy's  Book  of  Inventions.     Doubleday,  Page  &  Co.     (Elec- 
tric Furnace,  Electric  Light,  etc.) 

17.  The  Wireless  Man,  Collins.     Century  Company,  Philadelphia. 

18.  Historic  Inventions,  Holland.     Geo.  W.  Jacobs,  Phila.     (Bell, 
Edison,  Marconi.) 

19.  American  Inventions  and  Inventors,  Mowry.     Silver,  Burdett 
&  Co.     (Telegraph,  Telephone,  etc.) 

20.  Things  a  Boy  Should  Know  about    Electricity.    T.  M.  St. 
John,  New  York. 


PROJECT  XXIV 
RELATION  OF  LIGHT  TO  OUR  ABILITY  TO  SEE  THINGS 

WE  have  already  considered  the  great  source  of  our  light 
and  the  ways  in  which  we  produce  light.  Briefly  review 
this.  We  also  understand  the  importance  of  light  as  energy, 
and  its  relation  to  other  forms  of  energy.  Briefly  review 
your  knowledge  of  this.  In  this  chapter  we  shall  be  con- 
cerned chiefly  with  the  relation  of  light  to  our  ability  to  see 
things. 

Problem  1.  How  objects  are  visible.  —  Our  common 
experiences  prove  to  us  without  further  experiment  that 
light  must  be  present  in  order  to  see  objects.  Recall  ex- 
periences which  prove  this.  It  is  easy  to  understand  how  an 
object  which  produces  light  is  visible,  but  how  are  objects 
like  books,  chairs,  etc.,  visible?  When  light  strikes  an 
object,  a  book  for  example,  some  or  all  of  the  rays  of  light 
are  reflected. 


a  B 

FIGURE  215.  —  REFLECTION  OF  LIGHT  FROM  A  POLISHED  AND  A  MIRRORED 

SURFACE. 

Arrows  represent  the  relative  intensity  of  the  rays  of  light. 
276 


RELATION  OF  LIGHT   TO  OUR  ABILITY   TO  SEE      277 

If  the  surface  of  the  book  were  perfectly  smooth  (Fig- 
ures 215  and  216),  the  rays  would  all  be  reflected  in  the 
same  direction,  and  no  rays  would  reach  our  eyes  unless 
we  were  in  a  certain  location  (Figure  217).  The  cover  of 
the  book,  however,  is  not  so  smooth  as  it  appears  to  be, 


FIGURE  216.  —  REFLECTION  OF  LIGHT  FROM  A  SMOOTH  SURFACE. 

and  consequently  the  light  rays  striking  these  inequalities 
are  reflected  in  every  direction  (Figure  218)  in  straight  lines, 
so  that  rays  will  reach  our  eyes  regardless  of  our  position, 
providing  there  is  nothing  between  us  and  the  object  to 
intercept  the  rays. 

The  effect  of  the  inequalities  may  be  understood  by  throw- 
ing several  tennis  balls  together  upon  an  irregular  surface 
and  noting  the  directions  in  which  they  bounce.  The  rays 
of  light  which  pass  into  the  eye  from  an  object  form  an 


278 


GENERAL   SCIENCE 


image  or  picture  on  the  sensitive  inner  coat  of  the  eye,  the 
retina,  just  as  such  an  image  or  picture  is  formed  on  the 
sensitive  plate  or  film  of  a  camera.  In  some  way  which  we 
do  not  thoroughly  understand,  nerve  fibers  carry  to  the 
brain  information  of  impressions  made  by  the  light  on  the 
nerve  endings,  and  we  become  conscious  of  the  size,  color, 
and  shape  of  the  object. 

How  do  you  account  for  the  fact  that  a  room  may  be  light 
although  the  sun  does  not  shine  directly  into  it  ? 

Problem  2.     Cost  of  artificial  lighting  of  rooms.  —  Name 


FIGURE  217.  —  HELIOGRAPH. 

By  means  of  a  mirror  light  of  the  sun  is  reflected  to  a  place  many  miles 
distant.  Dots  and  dashes  of  the  telegraph  code  are  produced  by  a  shutter 
operated  by  the  sender  of  the  message. 

the  various  methods  of  producing  light  for  the  illumination 
of  rooms  when  sunlight  is  not  available.  We  are  especially 
concerned  with  the  comparative  costs  of  these  different 
kinds  of  lights.  To  determine  this,  we  must  be  able  to 
measure  the  intensity  of  a  light.  To  do  this  we  must  know 


RELATION  OF  LIGHT   TO  OUR  ABILITY   TO  SEE      279 


FIGURE  218.  —  REFLECTION  OF  LIGHT  FROM  A  SLIGHTLY  ROUGH  AND 

A  ROUGH  SURFACE. 

/' 

how  the  intensity  of  a  light  decreases  as  the  distance  from 
the  light  increases.  This  may  be  found  out  by  the  follow- 
ing experiment. 

Experiment.  —  Darken  a  room  except  for  one  small  source  of  light. 
Arrange  pieces  of  opaque  cardboard  respectively  1,  2,  and  3  inches 
square,  on  supports  so  that  they  can  be  moved  away  from  or  toward 


FIGURE  219.  —  RELATION  OF  INTENSITY  OF    ILLUMINATION  TO  DISTANCE  FROM 
SOURCE  OF  LIGHT. 

Compare  the  area  of  B  and  C  with  area  of  A.  What  is  the  intensity  of 
light  upon  one  of  the  squares  of  C  as  compared  with  intensity  upon  A~> 

the  source  of  light.  Place  the  1-inch  screen  one  foot  from  the  light 
and  place  the  second  screen  so  that  the  shadow  cast  by  the  first  just 
covers  it, 

In  the  same  way  place  the  third  screen  so  that  it  is  just  covered  by 
the  shadow.  Measure  the  distances  between  the  first  and  second  and 
the  second  and  third  screens.  What  is  the  relation  of  these  distances 


280  GENERAL  SCIENCE 

to  the  distance  between  the  source  of  light  and  the  first  screen  (Figure 
219)? 

If  the  first  screen  is  removed  it  is  evident  that  the  light  striking  the 
second  screen  is  the  same  that  illuminated  the  first  screen.  But  what 
is  the  area  of  the  second  screen  as  compared  with  the  first?  What, 
therefore,  will  be  the  intensity  or  brightness  of  the  light  on  the  second 
screen  as  compared  with  the  intensity  on  the  first  screen  ? 

In  the  same  way  compare  the  intensity  of  the  light  upon  the  third 
screen  with  that  on  the  first  screen.  What  conclusion  can  you  draw 
now  concerning  the  decrease  of  brightness  or  intensity  of  light  as  the 
distance  from  the  source  of  light  increases? 

Your  conclusion  may  be  stated  in  the  following  terms : 
The  intensity  of  light  is  inversely  proportional  to  the  square 
of  the  distance  from  the  light-giving  body. 

This  experiment  may  be  modified  by  substituting  for  the 
first  screen  a  larger  screen  in  which  is  cut  an  opening  one 
inch  square.  In  this  modification  of  the  experiment  the 
light-giving  body  should  be  surrounded  by  an  opaque  screen 
in  which  a  small  pinhole  has  been  made  so  that  the  light 
comes  from  a  point.  Unless  the  opening  is  very  small  the 
result  will  not  be  satisfactory. 

•The  principle  which  we  have  discovered  in  the  preced- 
ing experiment  may  be  used  hi  the  following  way  to  com- 
pare the  relative  light-giving  power  of  two  lights. 


FIGURE  220.  —  PHOTOMETER. 

An  apparatus  used  to  measure  the  comparative  light-giving  power 
of  two  lights. 

Experiment.  —  Place  the  lights  to  be  tested  several  feet  apart  on  a 
table  in  a  room  which  is  otherwise  dark.     Slide  an  upright  piece  of 


RELATION  OF  LIGHT   TO  OUR  ABILITY   TO   SEE       281 


FEE? 


opaque  cardboard  along  between  the  lights  until  no  shadow  is  cast  on 
either  side  of  the  cardboard  (Figure  220).  This  means,  of  course,  that 
there  is  an  equal  illumination  of  each  side  of  the  cardboard.  Since 
the  intensity  of  light  is  inversely  proportional  to  the  square  of  the 
distance  from  the  light-giving  body,  the  relative  power  of  the  two 
lights  may  be  calculated.  If,  for  example,  it  is  found  that  one  of  the 
lights  (a)  is  4  times  as  far  from  the  cardboard  as  the  other  (6),  then 
a:6::42:l2,  or  as  16:1. 

The  standard  of  measurement  of  the  light-giving  power 
of  a  light  is  called  a  candle  power.  This  was  originally  the 
light  given  by  a  candle 
made  according  to  cer- 
tain specifications.  At 
the  present  time  the 
value  of  the  candle 
power  in  the  United 
States  is  established  by 
a  set  of  standard  in- 
candescent lamps  main- 
tained in  the  Bureau  of  Standards  in  Washington.  Most 
incandescent  lamps  have  the  candle  power  etched  upon 
them.  It  can  be  seen  that  if  the  candle  power  of  one  light 

is  known  the  candle 
power  of  another  lamp 
may  be  determined  by 
the  experiment  above. 

Knowing     the     light- 
giving    power     of     two 

lamps,  it  is  possible   by 
FIGURE  222.  — GAS  METER  READING          ~     ,f       ,  '      . 

68700  FEET.  finding  how  rapidly  the 

oil  or  gas  (Figures  221 

and  222)  is  consumed  or  the  number  of  kilowatt  hours 
(Figure  223)  of  electricity  used,  and  the  price  charged,  to 


FIGURE  221.  —  GAS  METER  READING 
5700  FEET. 


»»•» 
E.J&J  .l| 


GENERAL  SCIENCE 


estimate  the  cost  per  candle  power  of  various  kinds  of 
lights.  The  following  table  (Figure  224)  has  been  worked 
out,  showing  the  relative 
cost  of  producing  a  cer- 
tain amount  of  light. 

Costs  have  been    based  KILOWATT  HOURS 

on   the  following  prices:    FIGURE  223. — FACE  OF  A  KILOWATT  HOUR 
Candles,    12    cents    per 

pound;    kerosene,    15   cents   per   gallon;    gas,    $1.00    per 
1000   feet;    and   electricity,.  10   cents  per  kilowatt  hour. 

Problem  3.  Why 
shades  and  reflec- 
tors are  used.  - 
The  effectiveness  of 
the  lighting  of  a  room 
may  be  increased 
by  the  proper  use  of 
shades  and  reflectors. 
In  lighting  a  room 
several  things  must 
be  kept  in  mind  : 
that  strong  direct 
rays  of  light  are  injurious  to  the  eyes;  that  in  some 

Inverted  Manila  Open  Flame  Upright  Manffe 


Candles 


Kerosene  Ffame 


Cos  Open  Ftame 
Gas  Mantle 
Carbon  Electric 
'Gem"  Elecfr/c 
Tungsten  > 


0         5         10        IS        20       25       30       3S      * 

Cost  of  IOOO  candle-hours  in  cents 
FIGURE  224.  —  RELATIVE  COSTS  OF  DIFFERENT 
LIGHTS. 


FIGURE  225.  —  COMPARATIVE  AMOUNTS  OF  LIGHT  GIVEN  BY  AN  OPEN 
GAS  FLAME  AND  A  GAS  MANTLE. 


RELATION  OF  LIGHT   TO  OUR  ABILITY   TO  SEE      283 


1  •  1  NUMERALS   REFER  TO  COST  PER   HOUR  IN  MILLS  (TENTHS  OF  A  CENT). 

cases   a    general    il- 


lumination  of  the 
room  is  desired  ;  and 
that  in  other  cases 
certain  parts  or  ob- 
jects in  the  room 
should  be  more  bril- 
liantly lighted. 

Give  examples 
showing  when  a 
general  illumination 
is  desired ;  when 
special  parts  of  the 
room  should  be  bet- 
ter lighted.  All 
these  aims  are  ac- 
complished by  means 
of  the  use  of  shades 
and  reflectors.  Can  you  recall  any  room  that  has  seemed 


ft* 


Regular  Upright  Mantle 


Junior  Upright  Mantle 


(Fish  Toll)  Burner— Turned  Do** 


Mantle  Pilot 


FIGURE  226.  —  COST  PER  HOUR  OF  DIFFERENT 
GAS  LIGHTS. 


FIGURE  227. 


FIGURE  228. 


Figures  237  £nd  228  shew  how  small  an  amount  of  light  passes  upward 
when  lights  are  shaded. 


284 


GENERAL   SCIENCE 


to  be  satisfactorily  lighted  in  which  there  was  not  some 
use  made  of  shades  or  reflectors? 


FIGURE  229.  —  REFLECTION  OF  LIGHT-BY  A  POLISHED  METAL  REFLECTOR. 

We  sometimes  hear  the  terms,  direct  and  indirect  lighting, 
used.     In  direct  lighting,  the  rays  are  reflected  in  one  general 


FfGURE  230. 

A,  reflection  and  transmission  of  light  by  opal  glass.    B,  reflection  of 
light  by  enameled  steel. 

direction  by  the  use  of  an  opaque  reflector  Figures  229  and 
230  B) .    Individual  reading  lamps  are  usually  of  this  type. 


RELATION  OF  LIGHT  TO  OUR  ABILITY   TO  SEE      285 

By  the  use  of  translucent  shades  which  permit  some  of  the 
rays  to  pass  through,  we  have  what  might  be  called  semi- 
direct  lighting  (Figures  227  and  230-4).  Many  halls  and 
meeting  rooms,  where  a  general  distribution  of  light  is 
desired,  have  opaque  or  partially  opaque  bowl  reflectors 
by  which  the  rays  of  light  are  directed  to  the  white  ceiling 
which  in  turn  reflects  them  downward  throughout  the  room. 
If  translucent  shades  are  used,  considerable  light  also 
passes  directly  outward  and  downward  from  the  lamp. 

Problem  4.  How  the  color  of  the  wall  affects  the  light- 
ing of  a  room.  —  We  'can  best  understand  the  relation  of 
th'e  color  of  the  wall  to  the  lighting  of  the  room  by  perform- 
ing a  simple  experiment. 

Experiment.  —  Obtain  or  make  a  pasteboard  cylindrical  box  from 
four  to  six  inches  in  diameter  and  a  foot  or  more  in  depth.  Paste  a 
picture  or  some  printed  matter  in  the  bottom.  Loosely  roll  a  piece  of 
white  paper,  slip  it  into  the  box  as  a  lining,  and  look  at  the  picture  or 
printed  matter.  Remove  the  white  paper  and  insert  a  roll  of  colored 
paper.  Do  this  successively  with  wall  paper  of  various  colors.  What 
is  the  effect  upon  the  illumination  of  the  interior  of  the  box  ? 

Make  a  list  of  the  wall  papers  in  the  order  of  their  value 
for  use  in  rooms  that  are  likely  to  be  dark.  Make  a  list 
of  wall  papers  in  order  of  their  value  for  use  in  rooms  that 
are  likely  to  be  too  light.  Compare  dirty  with  clean  wall 
paper  and  glazed  with  unglazed  paper  with  respect  to  their 
relation  to  illumination. 

You  have  seen  that  the  color  of  the  walls  makes  a  great 
difference  in  the  lighting  of  a  room.  Dark-colored  walls 
absorb  more  light,  and  hence  reflect  less  than  light- 
colored  walls.  Pure  white  walls  reflect  about  80  per  cent 
of  the  light  that  strikes  them ;  while  dark  green,  maroon, 
chocolate  brown,  or  dark  blue  walls  do  not  reflect  more 


286  GENERAL   SCIENCE 

than  about  5  per  cent  of  the  light  striking  them.  Smooth 
walls  reflect  more  light  than  those  which  are  rough.  Dirt 
upon  the  walls  reduces  their  power  of  reflection. 

Problem  5.  Why  objects  have  different  colors.  —  If  we 
see  the  various  things  around  us  by  reflected  light,  is  it  not 
rather  surprising  that  they  should  have  different  colors? 
The  light  which  comes  from  one  book  affects  the  nerve 
endings  in  the  eye  in  such  a  way  that  it  carries  a  message  to 
the  brain  which  gives  us  a  sensation  of  red ;  the  light  from  a 
book  beside  it  may  give  us  the  sensation  of  green.  The 
light  striking  the  books  must  be  the  same,  for  if  we  put  the 
red  book  where  the  green  one  was,  it  still  continues  to  be 
red.  Apparently,  therefore,  the  object  from  which  light 
is  reflected  causes  a  change  which  gives  rise  to  the  color. 

Another  illustration  of  the  production  of  color  by  light 
is  the  color  seen  at  sunset  and  sunrise.  What  colors  have 
you  seen  on  these  occasions  ?  Have  you  ever  seen  the  colors 
in  water  spray  when  looked  at  from  certain  positions,  or 
colors  along  the  edge  of  broken  glass?  What  are  the  colors 
of  the  rainbow  ? 

These  observations  all  indicate  that  ordinary  light,  which 
we  call  white  light,  may  be  broken  up  into  various  colors. 
The  truth  of  this  may  be  shown  by  the  following  experi- 
ment. 

1  Experiment.  —  Darken  the  room.  Place  a  glass  prism  in  such  a 
position  that  a  beam  of  sunlight  admitted  through  a  small  opening 
will  pass  through  it  (Figure  231).  What  do  you  observe  on  the  oppo- 
site wall? 

This  experiment  shows  that  white  light  is  really  a  com- 
bination of  the  colors  that  are  seen  in  the  rainbow.  We 
are  now  ready  to  understand  why  not  all  objects  are  white. 
When  light  strikes  the  wall,  for  example,  a  portion  of  it  is 


RELATION  OF  LIGHT  TO  OUR  ABILITY   TO  SEE      287 

absorbed,  and  a  portion  of  it  is  reflected.  You  have  noticed 
that  some  walls  reflect  more  light  than  others.  The  cover 
of  a  green  book  reflects  only  that  part  of  the  white  light 
which  gives  us  the  sensation  of  green;  a  red  book,  on  the 
other  hand,  absorbs  all  the  light  except  the  part  which  gives 
us  the  sensation  of  red. 


\ 


FIGURE  231.  —  BREAKING  UP  OF  LIGHT  IN  PASSING  THROUGH  A  PRISM. 

The  white  paper  of  this  page  reflects  almost  all  of  the  light 
which  strikes  it,  but  the  black  letters  absorb  practically 
all  the  light  which  strikes  them.  A  piece  of  red  glass  allows 
only  red  rays  to  pass  through ;  all  of  the  others  being  ab- 
sorbed or  in  some  cases  partially  reflected. 

Since  the  absorbed  light  is  changed  into  heat,  explain 
why  light-colored  clothing  is  more  comfortable  in  the  summer 
and  in  the  tropics,  and  dark-colored  clothing  is  preferred 
for  winter  wear.  Explain  why  the  colors  of  objects  may 
not  be  the  same  in  artificial  light  as  in  sunlight.  This  can 
be  shown  in  an  extreme  form  by  comparing  the  colors  of  a 
number  of  pieces  of  paper  or  cloth  when  observed  first  by 
sunlight,  and  then  by  a  candle  in  which  is  held  a  glass  rod 
which  has  been  dipped  in  common  salt  solution. 

Problem  6.    What  is  the  cause  of  the  colors  of  sunset 


288  GENERAL  SCIENCE 

and  sunrise  and  of  the  blueness  of  the  sky? — What  are  the 
chief  colors  of  sunset  and  sunrise?  In  the  experiment, 
in  which  by  means  of  the  prism  you  broke  up  white  light  into 
the  different  colors,  which  colors  were  bent  least,  and  which 
most,  from  the  original  path  of  the  light  ray?  The  at- 
mosphere, with  its  particles  of  moisture  and  dust,  has  some 
power  of  separating  the  colors  which  make  white  light. 
Explain  now  why  the  reds  and  oranges  are  seen  at  sunset 
and  sunrise.  Why  are  they  not  seen  at  midday  ? 

Keeping  in  mind  again  the  rays  that  are  bent  most  by 
the  prism,  and  the  fact  that  the  atmosphere  has  some  power 
to  separate  the  rays  which  compose  sunlight,  how  do  you 
account  for  the  blueness  of  the  sky?  This  can  be  illus- 
trated to  some  extent  by  putting  a  few  drops  of  milk  into  a 
jar  of  water  and  looking  through  the  jar  at  a  light.  Ex- 
plain why  the  sunsets  are  apt  to  be  most  brilliant  in  late 
summer  and  fall.  During  the  great  forest  fires  in  the 
northern  United  States  and  in  Canada,  the  sun  appeared 
orange  or  even  red  in  color.  Explain. 

Problem  7.  Why  eyeglasses  are  used  by  some  persons. 
—  You  all  know  people  who  without  glasses  must  hold  a 
book  very  close  to  the  eyes  in  reading.  These  nearsighted 
persons  have  trouble  in  seeing  distinctly  anything  which  is 
more  than  a  few  feet  from  them.  On  the  other  hand,  you 
may  have  friends  who  are  farsighted ;  who  can  read  signs 
at  a  greater  distance  than  you  can,  but  who  have  trouble 
in  reading  a  book  or  newspaper  held  at  the  ordinary  read- 
ing distance  from  the  eye.  Nearly  all  persons,  as  they  grow 
older,  become  farsighted ;  and  you  will  notice  that  many 
begin  to  wear  glasses  at  about  the  age  of  forty  or  even 
much  younger. 

By  the  use  of  glasses  both  the  nearsighted  and  the  far- 


RELATION  OF  LIGHT   TO  OUR  ABILITY   TO  SEE      289 

sighted  are  enabled  to  see  as  well  as  those  who  are  not 
troubled  by  these  eye  defects.  To  understand  how  glasses 
are  able  to  bring  about  this  change,  it  is  necessary  to  know 
how  the  rays  of  light  act  in  entering  the  eye. 

Sub-problem  1.     How  a  picture  or  image  is  formed  in  the 
eye.  —  The  following  diagram  (Figure  232)  represents  the  con- 


ch 


ch 


FIGURE  232.  —  RAYS  OF  LIGHT  PASSING  INTO  THE  EYE. 
/,  2,  extreme  points  of  the  object.     /',  2',  focus  of  rays  upon  sensitive 
layer  of  eye  (retina),     c,  cornea.     /',  iris,     ch,  choroid  (colored  coat  of 
eyeball).     /,  crystalline  lens,     o.n,  optic  nerve,  passing  from  eye  to  brain. 

dition  in  the  normal  eye.  It  will  be  noticed  that  the  rays  of 
light  are  bent  as  they  strike  the  curved  surface  of  the  cornea, 
and  again  as  they  pass  through  the  crystalline  lens,  finally 
coming  to  a  focus  on  the  nervous  layer,  the  retina,  lining  the 
back  of  the  eye  cavity.  This  is  the  same  process  that  takes 
place  in  a  camera  when  the  rays  of  light  coming  from  an 
object  are  bent  by  the  lens  of  the  camera  and  focused  on  the 
sensitive  film  or  plate. 

Sub-problem  2.  How  light  is  bent  in  passing  from  one 
substance  into  another.  —  The  ability  of  a  lens  to  bend  the 
rays  of  light  is  very  well  illustrated  by  a  burning  glass,  with 
which  the  parallel  rays  of  the  sun  may  be  focused  on  one  point, 
producing  enough  heat  there  to  burn  a  piece  of  paper. 


290 


GENERAL   SCIENCE 


The  effect  of  a  lens  upon  a  ray  of  light  may  be  understood 
from  the  following  diagram  (Figure  233). 

Light  may  be  considered  to  be  made  of  a  column  of  trans- 
verse vibrations.  These 
are  slowed  as  they  pass 
into  a  denser  substance  like 
glass.  You  can  easily  un- 
derstand how  the  column 
will  be  bent  if  the  glass 
is  entered  at  an  angle.  In 


FIGURE  233. —A  DIAGRAM  SHOWING  HOW 
A  LIGHT  RAY  MAY  BE  BENT. 


the  same  way,  as  the  ray 
of  light  passes  from  the 
glass  into  the  air  again,  it 
will  be  bent.  This  bending 
of  the  rays  of  light  (Fig- 
ure 234),  in  passing  from 
one  substance  into  another, 
called  refraction,  explains 
the  fact  that  a  stick,  projecting  at  an  angle  from  the  water, 
appears  to  be  bent  at  the  point  where  it  leaves  the  water. 

Sub-problem  3.  How  the  eye  is  able  to  focus  on  near  and 
distant  objects.  —  You  will 
wonder  how  we  can  focus 
the  eye  upon  a  distant  ob- 
ject, and  then  without  any 
appreciable  effort,  focus  it 
upon  something  near.  The 
power  of  accommodation 

may     be      illustrated    ,    as  FlGURE  234. -BENDING  OF  RAYS  OF  LIGHT 
follows.  BY  GROOVED  GLASS. 


Experiment.  —  Hold  a  pencil  before  your  eyes  and  read  the  label 
on  it.  How  does  a  picture  on  the  opposite  side  of  the  room  appear? 
Still  keeping  the  pencil  in  the  same  position,  look  at  the  picture.  How 
does  the  pencil  appear  now  ? 


RELATION  OF  LIGHT  TO  OUR  ABILITY   TO  SEE       291 

In  a  camera,  such  a  change  in  focus  is  brought  about  by 
moving  the  lens  closer  to  or  farther  from  the  sensitive  film. 
In  the  case  of  the  eye,  it  is  of  course  impossible  -to  change  the 
distance  between  the  lens  and  the  sensitive  inner  coat  of  the 
eye,  the  retina.  The  same  result,  however,  is  accomplished 
by  changing  the  shape  of  the  lens.  This  is  done  by  muscles 
which  are  connected  with  a  tough  membrane  or  ligament  in- 
closing the  lens.  The  muscle  by  its  contraction  flattens  the 
lens,  with  the  following  result. 

When  near  objects  are  to  be  looked  at,  the  muscles  relax 


FIGURE  235.  —  CHANGE  OF  Focus  OF  EYE. 

Upper  figure,  eye  focused  on  a  near  object.     Lower  figure,  eye  focused 
on  a.  distant  object. 

and   the  lens,  because  of  its  elasticity,  becomes  more  convex 
and  the  object  is  focused  upon  the  retina  (Figure  235). 

Sub-problem  4.  Cause  and  correction  of  farsightedness 
and  nearsightedness.  —  As  a  person  becomes  older,  the  lens 
loses  its  elasticity  and  it  becomes  impossible  for  him  to  see 
near  objects  distinctly,  although  his  power  of  seeing  things  at 


292  GENERAL   SCIENCE 

some  distance  remains  unimpaired.  You  can  easily  see  how 
the  use  of  slightly  convex  glasses  will  do  the  work  that  the 
flat  lens  of  his  eye  will  not  do,  enabling  him  to  see,  for  exam- 
ple, the  print  of  a  book  as 
well  as  before  the  lens  began 

Farsightedness,     not     the 
FIGURE  236.  —  FARSIGHTEDNESS  AND  ITS   result  of  age,  is  usually  due 
CORRECTION.  to    the    fact    that    the  eye- 

L,  lens.    /=  focus.  ball  is  too  short.     An  exam- 

ination of  the  diagram  (Figure  236)  will  show  that  a  distinct 
image  of  near  objects  cannot  be  formed  on  the  retina.  This 
condition  can  be  corrected  by  the  use  of  convex  glasses. 
Explain. 

Nearsightedness,  on  the  other  hand,  is  usually  caused  by  the 
eyeball  being  too  long.  In  this  case  the  image  of  an  object 
held  at  the  normal  reading  distance,  or  at  any  distance  farther 
away,  is  formed  in  front 
of  instead  of  on  the  retina. 
This  condition  can  be  cor- 
rected by  the  use  of.  con- 
cave eyeglasses  (Figure  23 7). 
Explain.  FIGURE  237.  —  NEARSIGHTEDNESS  AND  ITS 

CORRECTION. 
Sub-problem     5.       What 

is  astigmatism  and  how  is  it  corrected  ?  —  Many  persons 
who  are  neither  farsighted  nor  nearsighted  must  wear  glasses 
or  suffer  from  headaches.  This  is  caused  by  a  defect  of  the 
eye  called  astigmatism,  which  results  from  the  unequal  curva- 
ture of  the  cornea  (the  front  of  the  eyeball).  What  effect 
will  this  have  upon  the  bending  of  the  different  rays  of  light 
that  enter  the  eye?  The  glasses  for  these  eyes  are  curved 
in  such  a  way  that  the  defects  of  the  cornea  are  counter- 
acted. If  -  glasses  are  not  worn,  the  ciliary  muscle  in  its 
effort  to  bring  about  a  condition  which  will  result  in  a  clearer 
image  is  overworked  and  eyestrain  and  headache  result. 


RELATION  OF  LIGHT   TO  OUR  ABILITY   TO   SEE    •  293 

If  you  are  troubled  with  eyestrain  or  headache  after 
using  the  eyes  for  some  time,  have  your  eyes  examined  at 
once  by  a  competent  oculist  or  optometrist.  Eyestrain 
results  in  both  discomfort  and  lessened  efficiency.  Fre- 
quently headaches,  nervousness,  and  other  troubles  are 
relieved  as  by  magic  when  eyestrain  has  been  removed 
by  the  use  of  proper  glasses. 

Problem  8.    Advantage  of  having  two  eyes. 

Experiment.  —  Close  one  eye  and  attempt  to  put  the  cap  on  a 
fountain  pen  held  at  arm's  length.  With  one  eye  still  closed,  attempt 
to  put  a  pencil  into  a  hole  which  it  just  fits.  Try  the  same  things  with 
both  eyes  open.  Hold  a  book  several  feet  in  front  of  you,  with  its 
edge  toward  you.  Look  at  it  first  with  both  eyes  open,  then  alter- 
nately with  one  eye  closed  and  then  the  other.  What  are  the  results  ? 

Evidently  each  eye  forms  an  image  of  an  object  viewed 
from  a  slightly  different  angle.  The  effect  of  this  is  to 
give  us  a  sense  of  the  thickness  of  objects,  and  also  of  their 
distance  from  us.  The  brain  is  able  to  interpret  the  angle 
formed  by  the  rays  of  light  coming  from  the  object  to  the 
eyes,  and  consequently  we  are  conscious  that  one  object  is 
farther  from  us  than  another.  Pictures  viewed  with  an 
instrument  called  the  stereoscope  give  an  impression  of 
depth  and  distance  such  as  an  ordinary  photograph  fails  to 
give.  The  two  pictures  which  are  mounted  together  have 
been  taken  with  a  double  camera,  the  lenses  of  which  are 
the  same  distance  apart  as  the  human  eyes. 

Problem  9.  How  eyes  may  be  injured.  —  It  must  be 
remembered  that  although  the  eyes  are  in  perfect  condi- 
tion they  may  be  .abused,  and  eyestrain  with  its  accom- 
panying troubles  will  result.  Too  .continuous  focusing 
upon  close  work  tires  the  eye.  Occasionally  looking  away 
at  some  distant  object  for  a  few  moments  rests  the  eye  to  a 
surprising  degree. : 


294  •  GENERAL   SCIENCE 

Reading  by  a  dim  light  causes  overwork  of  the  muscles 
of  the  iris  in  their  effort  to  enlarge  the  pupil  to  admit  all  the 
light  possible.  The  image  is  indistinct  on  the  retina,  caus- 
ing one  to  hold  the  page  closer  to  the  eye,  throwing  an  ex- 
cessive amount  of  work  upon  the  ciliary  muscle.  One  is 
very  apt  to  abuse  the  eye  by  reading  in  the  evening  as  the 
light  is  fading;  the  eye  gradually  accommodating  itself 
to  the  lessening  light  until  a  condition  of  excessive  strain  is 
reached. 

Too  strong  a  light  is  almost  as  bad.  The  muscles  of 
the  iris  make  a  brave  effort  to  narrow  the  pupil  as  much  as 
possible  to  shut  out  the  excessive  light  which  is  tiring  the 
nerve  endings  of  the  retina. 

A  flickering  or  changing  in  the  intensity  of  the  light  com- 
ing to  the  eye  causes  constant  changes  in  the  eye.  From 
this  point  of  view  discuss  the  best  kind  of  light  to  be  used 
in  reading. 

Reading  on  street  cars  and  trains,  especially  at  night, 
often  results  in  headache  and  eyestrain.  Explain. 

The  reading  of  books  and  papers  printed  in  fine  type  or 
on  glossy  paper  is  highly  objectionable;  especially  is  small 
type  objectionable  in  books  used  by  young  persons. 

Serious  eye  diseases  have  been  contracted  by  those  who 
have  rubbed  their  eyes  with  their  fingers  after  having  been 
holding  to  a  strap  in  a  street  car  or  after  having  touched 
door  knobs  or  railings  which  have  been  handled  by  many 
persons.  Explain. 

Problem  10.  How  a  lens  makes  objects  appear  larger. 
—  The  action  of  a  reading  glass  or  a  .simple  lens  is  illus- 
trated by  the  following  figure. 

It  will  be  noticed  that  the  rays  of  light  come  to  the  eye 
at  the  same  angle  as  though  they  came  from  a  much  larger 


RELATION  OF  LIGHT   TO  OUR  ABILITY   TO  SEE      295 

object,  and  the  brain  thus  interprets  the  image  formed  on 
the  retina. 

In  the  case  of  the  compound  microscope,  the  rays  of 
light  before  reaching  the  eye  become  crossed,  and  also  enter 
the  eye  at  a  much  wider  angle ;  hence,  the  object  is  highly 
magnified  .and  appears  upside  down.  All  instruments  such 


FIGURE  238.  —  MAGNIFYING  GLASS. 

as  the  telescope,  opera  glasses,  and  projection  lanterns, 
which  are  used  to  give  us  a  magnified  appearance  of  an  ob- 
ject, depend  on  lenses  which  cause  the  light  coming  from  that 
object  to  enter  the  eye  at  a  much  wider  angle  than  if  the 
light  came  directly  from  it.  The  brain,  in  every  case,  in- 
terprets the  image  on  the  retina  as  though  these  wide- 
angled  rays  were  coming  directly  from  the  object. 

Problem  11.  How  motion  pictures  are  produced.  — The 
moving  picture  machine  which  has  come  to  play  such  an 
important  part  in  our  lives  in  giving  us  recreation  and  in- 
struction is  really  a  projection  lantern  in  which  the  pictures 
to  be  projected  are  very  small,  and  developed  on  a  roll  of 
transparent  celluloid  or  a  similar  substance. 

The  pictures  were  taken  by  a  camera  in  which  the  photo- 
graphic film  was  drawn  along  by  a  revolving  mechanism, 
thus  getting  a  succession  of  exposures  of  moving  objects, 
each  exposure  differing  slightly  from  the  succeeding  one, 


296 


GENERAL  SCIENCE 


FIGURE  239.  —  A  MOVING  PICTURE  FILM. 


RELATION   OF  LIGHT   TO  OUR  ABILITY   TO  SEE       297 

as  the  movement  progresses.  By  a  mechanism  similar  to 
that  used  in  taking  them,  the  successive  pictures  are  thrown 
upon  the  screen.  However,  we  do  not  see  them  as  separate 
pictures,  but  as  one,  in  which  the  motions  of  the  original 
subject  are  reproduced. 

The  way  in  which  a  succession  of  pictures  appears  as  one 
continuous  picture  is  well  illustrated  by  the  appearance  of 
the  spokes  of  the  wheels  of  a  rapidly  moving  automobile. 
Do  you  see  each  individual  spoke?  A  lantern  swung 
rapidly  in  a  circle  is  seen  as  a  circle  of  light.  It  is  evident 
that  the  image  of  an  object  does  not  disappear  immediately 
upon  the  disappearance  of  the  object. 

Problem  12.  How  light  effects  may  guide  us  in  the 
selection  of  clothing.  —  It  is  not  only  by  the  use  of  lenses 
that  our  sense  of  sight  may  be  deceived.  Have  you  ever 
noticed  that  one's  feet  look  larger  when  white  shoes  are  worn, 
that  stout  people  look  stouter  when  dressed  in  white,  and 
that  a  house  once  white,  which  has  been  painted  a  dark 
color,  appears  to  have  become  smaller  in  size? 


FIGURE  240. 

The  three  systems  of  lines  are  equally  distant  from  one  another  at 
all  points.     Do  they  appear  so  ? 

Certain  arrangements  of  lines  also  deceive  us.  A  stout 
person  appears  stouter  when  he  wears  clothes  which  have 
horizontal  stripes,  and  a  thin  person  appears  thinner  when 


298  GENERAL   SCIENCE 

he  wears  clothes  which  have  vertical  stripes.    The  way  in 
which  lines  deceive  us  is  illustrated  by  the  preceding  figure. 
Endeavor  to  explain  the  following  : 

1.  Why  ground  glass  or  glass  with  an  irregular  surface 
is  used  in  office  partitions. 

2.  Why  concave  mirrors  are  used  behind  headlights  of 
locomotives,  trolley  cars,,  etc. 

3.  Why  undimmed  automobile  headlights  are  not  usually 
permitted. 

4.  Why  corrugated   glass  is  used  in  automobile  head- 
lights. 

5.  Why  a  piece  of  glass  will  cast  a  shadow. 

6.  The  presence  of  a  wavy  appearance  over  a  hot  radia- 
tor or  stove,  or  over  a  dry  road  on  a  hot  day. 

7.  Why    colored    glasses    are    frequently    worn    at  the 
seashore  and  by  motorists. 

8.  Why  it  is  more  difficult  to  see  objects  when  you 
first  go  out  at  night  than  later. 

9.  Why  it  is  difficult  to  see  when  you  enter  a  brilliantly 
lighted  room  after  having  been  in  the  dark. 

10.  Why  the  inside  of  a  camera  is  painted  black. 

11.  Why  a  cake  of  ice  is  transparent,  and  a  block  of 
snow  is  not. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Determine  the  relative  candle  power  of  the  lights  in  your  home 
and  the  cost  per  candle  power. 

2.  Experiments  to  show  the  effect  of  color  of  walls  upon  the  illumi- 
nation of  a  room.     (Suggestion.      Use  long  narrow  boxes  with  dif- 
ferently colored  walls.) 

3.  Experiments  to  show  that  sunlight  may  be  broken  up  into  rays  of 
light  of  various  colors,  and  that  rays  of  light  of  various  colors  may  be 
combined  to  form  white  light. 


RELATION  OF  LIGHT  TO  OUR  ABILITY  TO  SEE       299 

4.  Demonstration  of  the  power  of  cloth  of  different  colors  to  absorb 
light,  and  change  it  into  heat. 

5.  Experiments  to  show  the  action  of  convex  lenses  in  correction 
of  farsightedness. 

6.  Demonstration  of  how  objects  are  made  to  appear  larger  by  the 
use  of  a  lens  or  reading  glass. 

7.  Demonstration  of  the  focusing  of  a  camera. 

8.  Demonstration  of  a  motion  picture  machine. 

9.  Demonstration  of  how  we  may  be  deceived  as  to  the  size  and 
shape  of  objects  by  the  arrangement  of  black  and  white  portions. 

REPORTS 

1.  Various  ways  in  which  eyes  may  be  injured,  and  care  that  must 
be  taken  for  their  protection. 

2.  The  lighting  of  factories  or  office  buildings. 

REFERENCES  FOR  PROJECT  XXIV 

1.  Stories    of    Inventors,    Doubleday.     Doubleday,    Page    &    Co. 
(How  Moving  Pictures  Came  to  Be.) 

2.  Wonders   of   Science.     Houghton   Mifflin   Company.     (Making 
Moving  Pictures.) 

3.  The  American   Boys'    Handy  Book,  Beard.     Scribners.     (Tele- 
scopes.) 

4.  Historic   Inventions,    Holland.     Geo.  W.    Jacobs,  Philadelphia. 
(Galileo  and  the  Telescope.) 

5.  American    Inventions  and  Inventors,  Mo  wry.     Silver,  Burdett 
&  Co.     (Torches,  Candles,  Kerosene,  Gas,  Electric  Lights.) 


PROJECT  XXV 


IMPORTANCE  OF  HEAT  TO  US 

THE  production  of  heat  and  its  relation  to  other  forms 
of  energy  have  already  been  considered.  Briefly  review 
your  knowledge  of  these  matters.  Some  of  the  ways  in  which 
problems  of  heat  affect  our  everyday  life  have  been  dis- 
cussed, but  there  still  remain  some  cases  which  need  further 
attention. 

Problem  1.  How  a  thermos  bottle  keeps  hot  liquids  hot 
and  cold  liquids  cold. 

Experiment.  • —  Fill  one  of  two  thermos  bottles  with  hot  water ; 
fill  the  other  with  cold  water.  Set  them  side  by  side  together  with  two 
ordinary  bottles  filled  respectively  with  hot  and  cold  water.  Examine 
after  two  or  three  hours.  Results  ?  Conclusion  ? 

An  explanation  of  the  structure  of 
the  thermos  bottle  (Figure  241)  will 
help  us  to  understand  its  ability  to  keep 
hot  things  hot  and  cold  things  cold. 

The  space  between  the  two  bottles  is 
a  vacuum ;  the  air  having  been  pumped 
from  it  during  the  process  of  manu- 
facture of  the  bottle.  Evidently  this 
vacuum  in  some  way  prevents  the  cool- 
ing or  warming  of  the  contents.  We 

FIGURE  241  — THER     can  understand  tnis  better  if  we  realize 
MOS  BOTTLE.          that   coldness   is   only   a    lack   of    heat, 

300 


Shook  AbBotbei 
Heavy  Glaai 


IMPORTANCE  OF  HEAT  TO   US 


301 


and  that  a  body  cools  because  heat  escapes  from  it.  It 
becomes  warm  because  heat  is  absorbed.  What  is  your 
conclusion  as  to  the  ability  of  heat  to  pass  through  a 
vacuum?  A  vacuum  is  called  a  poor  conductor  of  heat. 
The  polished  inner  surface  of  the  thermos  bottle  also  helps 
in  preventing  a  loss  of  heat,  since  heat  will  not  pass  as 
readily  from  a  highly  polished  surface  as  from  a  dull  sur- 
face. 

Problem  2.  How  food  may  be  cooked  in  a  fireless  cooker. 
—  Food  which  has  already  been  heated  to  the  boiling  point 
when  placed  in  a  fireless  cooker 
continues  to  cook  although 
no  additional  heat  is  applied. 
State  some  of  the  advan- 
tages of  such  an  apparatus. 
It  consists  of  two  boxes  of 
wood  or  metal,  one  inside 
of  the  other,  separated  by 
an  air  space  filled  with  excel- 
sior, sawdust,  newspapers, 
hay,  or  glass  wool  which  pre- 
vents the  circulation  of  air  (Figure  242).  What  are  your 
conclusions  concerning  the  power  of  still  air  and  the  sub- 
stances mentioned  to  conduct  heat  ? 

Refrigerator  walls  are  similar  in  their  construction  to  the 
walls  of  a  fireless  cooker.  The  space  between  the  walls  is 
usually  filled  with  charcoal. 

What  is  the  chief  use  of  clothing  in  winter?  What  kind 
is  usually  worn  then?  Explain  why  loosely  woven,  woolen 
clothing  is  warmer  than  that  which  is  tightly  woven  ?  Why 
are  fur  coats  so  warm  ?  In  the  summer  linen  is  the  coolest 
material  to  wear,  but  any  thin,  tightly  woven,  light-colored 
clothing  is  comfortable.  Explain. 


FIGURE  242.  —  FIRELESS  COOKER. 


302  GENERAL   SCIENCE 

Problem  3.  What  substances  are  good  and  what  are 
poor  conductors  of  heat. 

Experiment.  —  Place  in  a  cup  of  hot  water  a  silver  spoon  and  a  tin 
or  plated  spoon.  After  a  few  minutes  touch  the  handle  of  each.  Re- 
sult ?  Conclusion  ? 

Experiment.  —  Fill  a  test  tube  with  water  in  which  has  been  placed 
a  piece  of  ice  weighted  by  having  wire  wrapped  around  it.  Heat  the 
test  tube  near  the  top.  Result?  Conclusion? 

Recall  your  experiences  on  a  cold  morning  of  stepping 
on  a  bare  wood  floor ;  on  a  carpet ;  on  paper ;  or  on  a  tile  or 
stone  floor.  What  are  your  conclusions  as  to  the  power  of 
these  different  substances  to  conduct  heat  ? 

These  observations  are  sufficient  to  show  you  that  sub- 
stances differ  very  much  in  their  power  of  conducting  heat. 
The  metals  may  all  be  classed  as  good  conductors.  They 
may  be  ranked  in  the  following  order : 

1.  Silver  6.  Tin 

2.  Copper  7.  Iron 

3.  Aluminum  8.  German  Silver 

4.  Brass  9.  Mercury 

5.  Zinc 

Substances  which  are  medium  conductors  of  heat  are : 

1.  Rock  5.  Glass 

2.  Ice  6.  Water 

3.  Porcelain  7.  Plaster 

4.  Tiling 

Poor  conductors  of  heat  are : 

1.  Wood  5.  Wool 

2.  Asbestos  6.  Feathers 

3.  Paper  7.  Air 

4.  Cork 


IMPORTANCE  OF  HEAT  TO   US  303 

Explain  the  following : 

1.  Why  birds  ruffle  up  their  feathers  on  a  cold  day. 

2.  Why  a  light-weight  feather  or  down  coverlet  keeps 
one  so  warm. 

3.  Why  heat  pipes  in  basements  are  frequently  covered 
with  asbestos,  and  mats  of  this  material  are  used  under 
hot  dishes  at  the  table. 

4.  Why  asbestos  is  fastened  to  the  wall  behind  a  stove. 

5.  Why  newspapers  folded  under  the  coat  will  protect 
one  from  becoming  chilled  on  a  very  cold  day. 

6.  Why  the  thermos  bottle  is  stoppered  with  cork. 

7.  Why  the  water  in  deep  holes  in  a  lake  remains  cold 
during  the  hottest  part  of  summer. 

8.  Why  iron  is  better  than  brick  or  porcelain  for  stoves. 

9.  Why  bakers'  ovens  are  sometimes  inclosed  in  brick. 

10.  Why  tea-kettles  frequently  have  wooden  handles. 

11.  Why  oven  door  handles  are  usually  made  of  coiled 
wire. 

12.  Why  dead  air  spaces  are  left  between  the  walls  of  a 
building. 

13.  Why  building  paper  is  placed  in  the  wall  of  a  wooden 
house. 

14.  Why  the  outer  vessel  of  an  ice  cream  freezer  is  made 
of  wood. 

15.  Why  farmers  who  plant  wheat  in  the  fall  of  the  year 
are  glad  to  have  much  snow  in  winter. 

16.  Why  the  ticket  choppers  at  the  elevated  and  sub- 
way stations  keep  a  wooden  box  beneath  their  feet  in  cold 
weather. 

17.  Why  ice  is  packed  in  sawdust. 

18.  Why  on  a  very  cold  morning  outdoors  the  fingers 
will  freeze  to  the  metal  head  of  an  ax  but  not  to  the  wooden 
handle. 


304 


GENERAL   SCIENCE 


19.  Why  iron  is  a  good  material  for  steam  or  hot  water 
radiators. 

20.  Why  a  loosely  fitting  overcoat  is  warmer  than  one 
which  fits  tightly. 

Problem  4.  How  houses  are  heated.  —  Houses  may  be 
heated  by  stoves  or  fireplaces  which  are  located  in  all  or 
several  rooms.  Most  modern  houses,  however,  are  heated 
by  furnaces,  located  in  the  basement.  What  are  the  ad- 
vantages of  this?  Are  there  any  disadvantages?  The  heat 
produced  by  oxidation  of  fuel  in  the  furnace  is  distributed 
to  the  various  parts  of  the  house  by  hot  air  pipes  or  by 
pipes  carrying  steam  or  hot  water. 

Electrical  companies  are  now  producing  heaters  in  which 
electrical  energy  is  changed  into  heat  energy.  These  are 
especially  valuable  when  only  a  small  amount  of  heat  is 
needed  as  in  spring  and  fall.  How  are  trolley  cars  heated  ? 

Sub-problem  1.  How 
houses  are  heated  by  hot 
air.  —  A  hot  air  furnace 
(Figure  243)  is  essentially 
a  large  stove  around  which 
is  a  metal  jacket  through 
which  the  air  passes  to  be 
heated.  What  causes  the 
air  to  pass  through  the 
pipes  into  the  rooms  above? 
What  should  be  the  size 
of  the  intake  pipes  as  com- 
pared with  the  size  of  the 

FIGURE  243. -HOUSE  HEATED  BY  HOT  AIR.    Pi?68    carrying    air    from 

the    furnace?      In    order 

that  a  fresh  supply  of  air  may  enter  a  room,  there  must  be 
an  opportunity  for    the    air    already  there   to   escape.     How 


IMPORTANCE  OF  HEAT   TO    US 


305 


may  this  be  provided  for?  Hot  air  furnaces  sometimes  fail 
to  heat  satisfactorily  the  rooms  of  a  house  on  the  side 
against  which  a  strong  wind  is  blowing.  What  is  the  ex- 
planation of  this  fact  ? 

Some  hot  air  furnaces  not 
only  have  an  intake  pipe 
which  receives  air  directly  from 
outside,  but  also  a  pipe  which 
carries  air  from  the  first  floor 
back  to  be  heated  again.  Do 
you  think  such  an  arrangement 
is  good  or  bad  ?  Explain  your 
answer. 

Do  you  think  that  hot  air 
heating  would  be  a  good  method 
of  heating  large  apartment 
houses?  Why? 

The  extreme  heat  of  the 
firebox  may  cause  a  warping 
and  cracking  of  the  iron  plates 
of  its  walls.  Explain  why  gas 
from  the  burning  coal  some- 
times comes  up  through  the 
hot  air  pipes.  This  is  not 
usually  the  case  when  the 
damper  in  the  flue  is  so  ar- 
ranged that  the  draft  is  not 
interfered  with.  Explain. 

Sub-problem  2.  How  houses 
are  heated  by  hot  water  (Figure  244) .  —  What  causes 
the  water  to  rise?  (Water  expands  when  heated.)  Why 
is  it  necessary  to  have  the  tank  in  the  attic?  Must  the 
pipes  be  full  of  water?  Why?  What  precautions  must  be 
taken  if  the  house  is  left  unoccupied  in  the  winter?  The 
radiator  (R),  just  as  a  stove,  heats  a  room  in  two  ways;  by 


FIGURE  244.  —  HOUSE  HEATED  BY 
HOT  WATER. 

In  what  direction  is  water  moving 
in  pipe  £?  in  0?  Why  is  the  tank 
B  in  the  attic  necessary  ? 


306  GENERAL   SCIENCE 

radiation,  the  giving  out  of  heat  directly,  and  by  setting  up 
air  currents  as  was  discussed  in  the  study  of  ventilation. 

Sub-problem  3.  How  houses  are  heated  by  steam.  —  In 
a  steam  heating  plant,  steam  instead  of  water  passes  through 
the  pipe  into  the  radiator.  This  steam  in  the  radiator  con- 


•I 


FIGURE  245.  —  CIRCULATION  OF  WATER,   IN  THE   RADIATOR  AND  AROUND 
THE  CYLINDERS  OF  AN  AUTOMOBILE. 

The  reasons  for  the  circulation  of  water  here  are  the  same  as  in  the 
pipes  and  boiler  of  a  hot  water  heating  plant. 

denses  into  water.  How  does  this  fact  affect  the  heating  of  the 
room  ?  Should  the  boiler  of  a  steam  heating  plant  be  filled  with 
water?  Why?  Explain  the  need  for  the  safety  valve  of  the 
boiler.  Explain  why  on  days  when  only  a  small  amount  of  heat 
is  needed  in  the  house,  steam  heat  is  not  so  satisfactory  as 
either  hot  air  or  hot  water  heat.  Explain  why  rooms  heated 


IMPORTANCE  OF  HEAT  TO   US  307 

by  steam  cool  off  much  more  rapidly  after  the  fire  is  shut  down 
at  night  than  rooms  heated  by  hot  water. 

Explain  why  in  all  furnaces  the  opening  of  the  door  below 
the  firebox  makes  the  fire  burn  better,  and  why  the  opening 
of  the  coal  door  checks  the  fire. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Make  a  fireless  cooker. 

2.  Find  out  the  value  of  different  kinds  of  clothing  in  preventing 
the  escape  of  heat  from  the  body.     (Suggestion.     Cover  bottles  con- 
taining hot  water  with  various  combinations  of  cloth,  and  observe  how 
soon  the  water  becomes  cool.) 

3.  Determine  by  experiments  the  power  of  different  substances  to 
conduct  heat. 

4.  Study  the  plan  of  the  heating  system  of  your  house  and  make  a 
diagram  of  it.     Explain  the  reason  for  the  arrangement  and  the  use  of 
various  devices. 

REPORTS 

Describe  the  methods  of  heating  houses  in  different  countries, 
including  the  kinds  of  fuel  used. 

REFERENCES  FOR  PROJECT  XXV 

1.  The  Fireless  Cooker.     Farmers'  Bulletin  No.  771  U.  S.  Depart- 
ment of  Agriculture. 

2.  Shelter  and  Clothing,  Kinne  and  Cooley.     Macmillan  Company. 

3.  The  Thermometer  and  Its  Family  Tree.    Taylor  Instrument 
Company,  Rochester,  N.  Y.     l(ty. 

4.  Chemistry  of  Common  Things,  Brownlee,  Fuller,  and  others. 
Allyn  and  Bacon 


UNIT  V 

RELATION   OF   SOIL  AND  PLANT  LIFE  TO  EVERYDAY 
ACTIVITIES 

PROJECT   XXVI 
HOW  SOIL  IS   MADE 

WE  have  already  seen  how  plant  life  is  essential  to  animal 
life  upon  the  earth.  Without  plant  life  therefore,  there  could 
be  no  human  life  upon  the  earth.  Explain.  In  this  unit 
we  shall  consider  projects  and  problems  concerned  with  the 
production  of  plants. 

The  working  out  of  these  projects  and  the  solution  of  the 
problems  that  arise  will  in  many  cases  help  us  to  solve  impor- 
tant problems  of  animal  and  human  life. 

Since  the  growth  of  plants  is  dependent  on  soil  it  is  evident 
that  we  must  consider  the  projects  how  soil  is  formed  and 
how  it  is  related  to  plants.  Other  projects  will  naturally 
be  how  plants  and  animals  make  use  of  the  manufactured 
food  in  their  growth,  how  plants  produce  seed,  how  better 
plants  and  animals  are  produced,  and  how  plants  are  pro- 
tected from  harmful  insects. 

It  is  known  that,  if  we  go  back  far  enough  in  the  world's 
history,  there  was  once  a  time  when  there  was  no  soil.  The 
wnole  surface  of  the  earth  was  rock,  just  as  we  find  the 
earth's  crust  if  we  dig  down  through  the  soil.  An  examina- 
tion of  soil  may  give  us  some  hints  which  will  help  us  to 
understand  how  it  has  been  formed. 

308 


HOW  SOIL  IS  MADE  309 

Problem  1.  Of  what  is  soil  composed? — Examine  a 
handful  of  dry  soil.  Do  you  find  any  particles  of  sand  in  it  ? 
What  is  sand?  Examine  a  very  small  amount  of  it  with  a 
magnifying  glass  or  microscope.  What  do  you  find  ?  Some- 
times soils  have  so  many  small  pieces  of  rock  that  they  are 
called  gravelly  soils  or  sandy  soils.  What  do  you  suspect 
is  the  origin  of  the  sand  or  gravel  ?  What  is  the  color  of 
soil?  Where  have  you  ever  seen  soil  that  is  very  dark  in 
color?  Can  you  suggest  a  possible  explanation  for  this 
color  ? 

Experiment.  —  Heat  some  soil  from  a  flower  pot  in  a  crucible  or  in 
a  test  tube  if  you  have  no  crucible.  What  change  in  color  appears 
first?  Of  what  does  the  odor  that  is  given  off  remind  you?  What 
change  in  color  occurs  after  continued  heating?  The  material  which 
remains  after  continued  burning  is  called  mineral  matter.  From  your 
observations  what  do  you  consider  to  be  the  composition  of  the  soil, 
and  from  what  do  you  think  it  has  been  formed? 


FIGURE  246.  — RELATIVE  SIZE  OF  SOIL  PARTICLES  (all  highly  magnified). 
From  left  to  right :  clay,  silt,  sand,  gravel. 

Plants  cannot  grow  unless  air  and  water  are  present  in  the 
soil.  A  good  soil,  therefore,  consists  of  decomposed  rock 
material,  60  to  05  per  cent  of  its  weight,  together  with 


310  GENERAL   SCIENCE 

humus,  bacteria,  air,  and  moisture.     The  materials  which 
make  up  soils  may  be  classed  as  follows  (Figure  246) : 

(a)  Humus,  or  vegetable  mold. 

(b)  Clay,  made  up  of  finely  powdered  rock.     The  particles 
are  less  than  one  ten-thousandth  of  an  inch  in  diameter.     When 
dry,  clay  is  powdery ;   when  wet,  it  is  sticky. 

(c)  Silt,  consisting  of  particles  somewhat  coarser  than  clay. 
When  moist  it  becomes  a  soft  mud  and  usually  crumbles  when 
it  is  dry. 

(d)  Sand,  made  of  rock  fragments. 

(e)  Gravel,  composed  of  large  pieces  of  rock  fragments. 
Ordinary  soils  are  usually  made  up  of  a  mixture  of  clay, 


FIGURE  247.  —  DISINTEGRATION  OF  ROCK. 
Limestone  ledge  breaking  up  and  forming  soil. 

sand,  silt,  and  humus.  Since  moisture  is  so  necessary  to 
plants,  the  power  of  a  soil  to  take  up  and  hold  water  is  a 
very  important  characteristic  of  it. 

Problem  2.     Evidence  that  soil  is  now  being  formed.  — 
Apparently  a  portion  of  the  soil  has  been  formed  from  rock. 


HOW  SOIL  IS  MADE 


311 


If  this  is  so,  then  there  should  be  indications  that  such  a 
change  is  going  on  at  the  present  time.  An  examination 
of  the  side  of  a  railroad  cut  will  usually  show  gradations 
from  solid  rock,  through  partially  disintegrated  rock,  to 
well-formed  soil.  The  accompanying  picture  (Figure  247) 

shows  rocks    of  various   . , 

sizes  which  have  been 
broken  off  from  the 
great  mass  of  rock.  Old 
marble  gravestones  with 
their  rounded  edges  and 
more  or  less  indistinct 
lettering  are  indications 
that  rock  may  be  worn 
away.  These  evidences 
coupled  with  the  fact 
that  pebbles  and  small 
fragments  of  rocks  are 
found  in  soils  indicate 
that  the  process  of  soil 
making  is  still  going  on. 

Problem  3.  How  soil 
has  been  produced  by 
weathering.  —  Some  of 
the  agencies  that  change 
rock  into  soil  can  easily 
be  understood.  Break  a 
rock,  and  compare  the 

broken  surface  with  the  surface  of  the  rock  which  has 
been  exposed  to  the  weather.  What  is  your  conclusion  ? 

The  oxygen  of  the  air  may  act  upon  some  of  the  minerals 
of  the  rocks  causing  a  change  which  results  in  their  crumbling. 


FIGURE  248.  —  RUGGED  MOUNTAINS  SHOW- 
ING THE  EFFECT  OF  WEATHERING. 


312 


GENERAL   SCIENCE 


This  is  similar  to  the  action  of  oxygen  in  causing  the  rusting 
of  iron.  Carbon  dioxide  dissolved  in  water  is  one  of  the 
most  efficient  agents  in  the  breaking  down  of  rocks.  It  is 
the  action  of  carbon  dioxide  in  water  which  has  produced 
the  great  caves  such  as  Luray  Cave  in  Virginia,  Mammoth 
Cave  in  Kentucky,  and  Wyandotte  Cave  in  Indiana,  as  well 
as  hundreds  of  smaller  ones  in  various  parts  of  the  country 
where  limestone  is  the  common  rock.  This  action  can  be 
shown  by  passing  carbon  dioxide  through  water  containing 
a  small  amount  of  finely  powdered  marble. 

What   do    you    think 

might  be  the  effect  upon 
some  rock  of  alternate 
heating  and  cooling 
caused  by  the  tem- 
perature changes  of  day 
and  night? 

Experiment. — Heat  a  glass 
tube  and  plunge  it  into  cold 
water.  What  happens?  The 
cracking  of  the  rocks  by 
this  means  exposes  more  sur- 
face for  the  action  of  the 
weather. 

What  will  happen  in 
cold  weather  to  the  water 
which  is  in  the  crevices 
of  the  rock?  What  ef- 
fect will  this  have  upon  the  rock?  This  can  be  illustrated 
by  exposing  to  a  freezing  temperature  a  tightly  stoppered 
test  tube  filled  with  water.  The  force  due  to  the  expan- 
sion of  water  when  it  changes  into  ice  causes  the  bursting 


FIGURE  249.  —  WEATHERED  ROCK  AT  BASE 
OF  A  CLIFF. 


HOW  SOIL  IS  MADE 


313 


of  water  pipes  and  the  ruin  of  automobile  radiators,  if 
cars  are  permitted  to  remain  in  unheated  garages  in  very 
cold  weather  without  removal  of  the  water.  (This  latter 
may  be  prevented  by  adding  to  the  water  in  the  radiator 
some  substance,  alcohol 
for  example,  which  has 
a  lower  freezing  point.) 

The  great  masses  of 
broken  rock  at  the  foot 
of  cliffs  (Figure  249),  as 
at  the  base  of  the  Pali- 
sades along  the  Hudson 
River,  are  caused  very 
largely  by  the  final 
breaking  off  of  pieces 
of  rock  by  the  expan- 
sion of  freezing  water 
which  has  gotten  into 
the  crevices  formed  by 
temperature  changes. 
Roots  of  trees  growing 
in  the  crevices  of  rocks 
also  assist  in  the  further 
splitting  of  the  rocks 
(Figures  250  and  251). 

Problem  4.     How  soil 
has   been   produced  by 
water     and    wind    ero- 
sion. —  Water    erosion.  —  The    fragments    of    rock,    pro- 
duced   by    the    processes    mentioned    above,  are    carried 
along  by  the  swiftly  moving  water  of  rivulets  and  streams. 
What  will  be  the  effect  upon  the  bottom  of  such  streams? 


314 


GENERAL  SCIENCE 


What  will  be  the  effect  upon  the  fragments  themselves? 
What  is  the  shape  of  pebbles  and  rocks  found  in  a  stream  ? 
Why?  Explain  how  the  valleys  of  streams  have  been  cut 
down  through  the  rock.  This  action  of  water  carrying 
fragments  of  rock  is  called  erosion  (Figure  252).  It  is  ex- 
actly similar  to  the  way 
in  which  a  grindstone  is 
able  to  sharpen  tools; 
both  the  grindstone  and 
the  metal  of  the  tool  are 
worn  away.  As  the 
streams  become  less  swift 
much  of  the  material  is 
deposited,  so  that  soil  is 
constantly  being  eroded 
from  the  more  elevated 
regions  and  deposited  in 
the  lowlands. 

Wind  erosion.  —  In 
some  parts  of  the  world 
considerable  erosion  is 
done  by  wind  carrying 


FIGURE  251.  —  BEECH  TREE    GROWING  ON 
ROCKS. 

The  roots  penetrate  into  crevices  and  by  their 
growth  split  the  rocks. 


sand  in   the   same  way 

that  a  sand  blast  is  used  in  etching  glass  or  in  cleaning  the 
surface  of  a  stone  building.  Wind,  however,  as  an  agent 
in  the  formation  of  soil  is  of  very  little  importance  in  com- 
parison with  those  already  mentioned. 

Problem  5.  How  most  of  the  soil  of  northern  United 
States  has  been  produced.  —  In  the  northern  part  of  our 
country,  pebbles  and  rocks  of  all  sizes,  unlike  the  solid  rock 
bed  of  that  region,  are  frequently  found  imbedded  in  the  soil 
(Figure  253).  Evidently  the  soil  and  rocks  of  those  regions 


HOW  SOIL  IS  MADE  315 

have  not  been  carried  there  by  water,  since  the  rocks  are 
scattered    indiscriminately  in  the  fine  soil  (clay).     Explain 


FIGURE  252. — WATER  EROSION. 

Gravel  and  rock  have  been  eroded  from  the  higher  land  and  carried 
down  by  water. 


FIGURE  253.  —  SOIL  DEPOSITED  BY  A  GLACIER. 
Note  the  irregularly  shaped  boulders. 


316 


GENERAL   SCIENCE 


the  reason  for  this  conclusion.  On  examination  many  of 
the  rocks  are  found  to  have  scratches  on  them  (Figure  254). 
Also  if  the  soil  is  removed,  the  surface  of  the  country  rock 
will  be  found  to  have  deep  parallel  scratches  and  grooves. 

Many  thousands  of  years  ago,  a  great  sheet  of  ice,  called  a 
glacier,  covered  the  northern  part  of  the  United  States  (Fig- 
ure 255).  As  it  moved  southward,  its  immense  weight  broke 
off  fragments  of  rock  which  rubbed  along  the  bottom  of  the 
glacier  and  ground  up  the  rocky  bed  into  a  finely  powdered 


FIGURE  254.  —  ROCK  SHOWING  GLACIAL  SCRATCHES. 

soil  (clay)  leaving  great  scratches  and  grooves.  The  clay 
and  the  boulders,  or  rocks,  became  thoroughly  mixed  in 
the  ice.  As  the  glacier  reached  its  southern  extent,  it 
melted  and  the  material  in  it  was  deposited  there  as  a 
series  of  ridges  of  hills  called  a  terminal  moraine  (Figure 
257). 

As  the  glacial  period  gradually  passed,  the  glacier  was 
unable  to  push  farther  south  and  as  a  result  a  series  of  these 
moraines  have  been  formed.  When  the  entire  ice  sheet 


HOW  SOIL  IS  MADE 


317 


melted,  the  rock  and  soil  carried  by  it  was  left  wherever  it 
happened  to  be.  As  some  parts  of  the  glacier  carried  a  large 
quantity  of  material  and  other  parts  only  a  small  amount, 


FIGURE  255.  —  EXTENT  of  ICE  SHEET  DURING  GLACIAL  PERIOD. 


a  layer  of  rock  and  soil  of  unequal  thickness  was  deposited 
over  all  the  northern  parts  of  the  country.  The  depressions 
became  filled  with  water  and  thus  the  large  number  of  the 
lakes  of  these  northern  states  is  accounted  for. , 


318  GENERAL  SCIENCE 

Problem  6.  How  soil  has  been  produced  by  decay  of 
organic  matter.  —  Plants  gain  a  foothold  in  the  soil  formed 
by  the  decomposition  of  rock  material  and,  by  their  own 
decay  and  that  of  animals  which  live  upon  them,  add  to 
the  soil  that  part  of  it  which  causes  it  to  blacken  when 


FIGURE  256.  —  A  GLACIER. 
Glacier  flowing  down  side  of  Mt.  Robson,  British  Columbia. 

burned.  This  organic  part  of  the  soil,  or  humus  (Figure 
258),  is  of  special  importance  in  giving  it  the  proper  texture 
and  increased  power  of  holding  water.  It  is  also  the  prin- 
cipal source  of  nitrogen  which  is  so  necessary  for  plant 
growth.  If  you  will  recall  your  study  of  bacteria,  you  will 
remember  that  they  are  necessary  in  soils  in  order  to  decom- 
pose the  vegetable  and  animal  matter  so  that  this  material 
may  be  used  again  in  the  growth  of  plants. 


FIGURE  257.  — FRONT  OF  A  GLACIER,  Mr.  RAINIER  NATIONAL  PARK. 

Notice  the  broken  rock  which  was  carried  down  and  deposited  when  the 

glacier  extended  somewhat  farther  into  the  valley. 


FIGURE  258.  —  FORMATION  OF  HUMUS. 

Vertical  section  showing  forest  floor,  humus,  soil,  and  roots. 
319 


320  GENERAL  SCIENCE 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Collect  and  put  into  test  tubes  specimens  of  different  kinds 
of  soils,  including  rock  and  vegetable  material  which  has  partially 
changed  into  soil. 

REPORTS 

1.  Evidences  in  the  United  States  of  the  glacial  periociu 

2.  Description  of  a  glacier. . 

3.  Character  of  the  soil  in  different  parts  of  your  state. 

REFERENCES  FOR  PROJECT  XXVI 

1.  Glaciers  of  North  America,  J.  C.  Russell.     Ginn  &  Co. 

2.  Soils ;  Their  Properties  and  Management,  T.  L.  Lyon.     Mac- 
millan  Company. 

3.  Agronomy,  Clute.     Ginn  &  Co. 

4.  Story  of  Agriculture    in  the  United  States,  A.    H.  Sanford. 
D.  C.  Heath  &  Co. 

5*.    Essentials  of  Agriculture,  H.  W.  Waters.     Ginn  &  Co. 

6.  The  Land  We  Live  In,  O.  W.  Price.     Small,  Maynard&  Co. 

7.  Earth  and  Sky  Every  Child  Should  Know,  J.  E.  Rogers. 
Doubleday,  Page  &  Co. 

8.  The    United   States,    J.  O.  Winston.      D.  C.  Heath  &  Co. 
(The  Great  Glacier  and  Its  Effect.) 

9.  Wonders  of  Science.     Houghton  Mifflin  Company. 

10.  Farm  Science,  W.  J.  Spellman.     World  Book  Company. 

11.  Elementary  Agriculture,  James  S.  Grim.     Allyn  and  Bacon. 


PROJECT  XXVII 
RELATION   OF   SOIL  TO   PLANTS 

SINCE  the  amount  of  moisture  in  the  soil  has  a  great  effect 
upon  the  growth  of  plants  one  important  problem  is :  how 
the  water-holding  power  of  the  soil  may  be  increased.  As 
the  project  is  further  analyzed  it  will  be  seen  that  other 
problems  will  be  those  concerned  with  what  plants  take 
from  the  soil,  how  these  substances  may  be  returned  to  the 
soil,  how  materials  are  taken  from  the  soil  and  what  the 
plant  does  with  this  material. 

Problem  1.  How  the  water-holding  power  of  the  soil 
may  be  increased.  —  We  all  know  from  observation  that 
the  growth  of  plants  depends  upon  their  being  able  to 
get  sufficient  water  from  the  soil.  How  does  grass  appear 
during  a  prolonged  dry  period  in  summer?  How  may 
lawns  and  parks  be  kept  green  during  such  a  time?  We 
may  water  a  small  garden  by  the  use  of  a  hose,  but  such 
a  means  of  supplying  water  to  a  large  field  is  impossible. 
Therefore,  any  method  by  which  the  water-holding  power 
of  soil  may  be  improved  is  very  important. 

The  water  which  is  taken  from  the  soil  by  plants  may 
have  two  sources.  It  may  be  from  water  which  has  recently 
fallen  as  rain  or  it  may  be  from  water  which  has  come  up 
through  the  soil  from  below.  A  hole  dug  in  the  soil  during 
dry  weather  will  show  that  the  upper  part  of  the  soil  is  dry 
and  that  the  lower  part  is  moist.  If  you  lift  either  a  board 
or  a  stone  which  has  been  undisturbed  for  a  considerable 
time,  what  is  the  condition  of  the  soil  beneath  it  ?  What  is 

321 


322 


GENERAL   SCIENCE 


the  condition  of  the  soil  under  a  layer  of  leaves  or  straw 
which  has  been  lying  in  one  place  for  a  long  time? 

During  dry  weather  lay  a  board  on  freshly  cultivated 
earth  in  the  garden,  and  in  a  few  days  compare  the  appear- 
ance of  the  surrounding  soil  with  that  under  the  board. 
All  of  these  observations  indicate  that  the  water  which  is 
coming  from  below  is  escaping  by  evaporation  at  the  surface 
and  that  the  loss  may  be  prevented  by  a  covering  of  some 
kind.  Sometimes  such  a  covering  is  provided  by  a  layer 


FIGURE  259.— VACANT  LOT  GARDEN. 
Give  two  seasons  for  hoeing  a  garden. 

of  leaves  called  a  leaf  mulch.  But  usually  such  a  method 
cannot  be  employed  very  extensively.  It  has  been  found 
that  hoeing  (Figure  259)  or  "  cultivating  "  by  making  a 
mulch  of  dry  soil  prevents  to  a  great  extent  this  escape 
of  water  at  the  surface.  This  is  because  the  small  capil- 
lary spaces  through  which  the  water  has  been  coming  from 


RELATION  OF  SOIL   TO  PLANTS 


323 


below  are  broken  up.  One  of  the  reasons,  therefore,  for  fre- 
quent hoeing  of  a  garden  or  cultivating  of  a  field  of  corn  is 
to  prevent  the  loss  of  moisture  from  the  surface  of  the  soil. 
The  power  of  different  kinds  of  soils  to  absorb  water  from 
below  may  be  illustrated  by  the  following  experiment. 


Experiment.  —  Over  the  bottom  of 
each  of  four  or  five  glass  tubes  having 
a  diameter  of  one  or  two  inches,  tie 
a  piece  of  cheesecloth  (Figure  260). 
Fill  the  different  tubes  with  the  fol- 
lowing kinds  of  soil :  coarse  sand,  fine 
sand,  loam,  and  clay.  Place  the  bot- 
toms of  the  tubes  in  a  vessel  of  water, 
and  support  them  so  that  they  will 


a  a  a  D 


FIGURE  260.  —  ABSORPTION    OF 
WATER  BY  SOILS. 

stand  upright.     After   a   day    examine     From  left  to  right :  loam,  clay, 


the  tubes  and  draw  conclusions. 


fine  sand,  coarse  sand. 


The  finer  the  soil  the  smaller  are  the  openings  through 
which  the  water  passes.  How  does  this  experiment  help 
you  to  explain  the  effectiveness  of  the  loose  soil  mulch? 
How  does  it  explain  the  fact  that  seeds  will  grow  better  if 
the  earth  is  pushed  down  firmly  around  them  ? 

The  power  of  soils  to  hold  the  rain  which  falls  upon  them 
is  shown  by  the  following  experiment. 

Experiment.  —  Into  four  funnels  in  each  of  which  has  been  placed 
filter  paper,  put  equal  amounts  of  different  soils  :  coarse  sand,  fine  sand, 
loam,  and  clay.  Pour  into  the  funnels  equal  amounts  of  water.  Catch 
the  water  that  runs  through  in  measuring  glasses.  After  pouring  the 
water  through  several  times,  note  the  amount  of  water  that  runs 
through  each  and  draw  your  conclusions  as  to  the  conditions  which 
make  soils  good  holders  of  water.  Suggest  how  the  ability  of  the  soil 
of  a  garden  to  hold  moisture  may  be  increased. 

•  Problem  2.    What  plants  take  from  the  soil.  —  Chemical 
analysis  of  plants  and  experiments  in  their  culture  indicate 


324  GENERAL   SCIENCE 

that  the  following  ten  elements  are  necessary  for  their 
growth:  Carbon,  hydrogen,  oxygen,  nitrogen,  potassium, 
magnesium,  calcium,  iron,  sulphur,  and  phosphorus.  In  our 
study  of  the  making  of  starch  and  wood  by  plants,  we  have 
already  discovered  from  what  source  the  plant  gets  its 
carbon,  hydrogen,  and  oxygen.  Review  and  explain.  All 
the  other  elements  must  come  from  the  soil. 

Fortunately,  the  soil  usually  contains  all  of  these  with  the 
exception  of  three,  in  such  quantities  that  there  is  not  much 
danger  of  them  being  exhausted.  The  three  which  are 
likely  to  be  lacking  are  nitrogen,  potassium,  and  phosphorus. 
These  frequently  have  to  be  added  to  the  soil  in  some  way. 

Problem  3.  How  nitrogen  may  be  given  to  the  soil.  — 
Nitrogen  is  found  largely  in  the  organic  part  of  the  soil,  and 
Konsequently  the  addition  of  plant  and  animal  material 
will  increase  the  stock  of  nitrogen.  One  form  of  organic 
matter  put  upon  the  soil  is  horse  manure.  In  some  parts 
of  the  country,  fish  which  are  useless  for  food  are  spread  over 
the  fields.  It  is  said  that  the  early  American  explorers 
found  that  the  Indians  placed  a  fish  in  each  hill  of  corn. 

Waste  from  slaughter  houses;  guano,  the  excrement  of 
countless  generations  of  sea  birds ;  cottonseed  meal ;  linseed 
meal,  etc.,  are  useful  sources  of  nitrogen.  The  nitrogen  in 
none  of  these  plant  or  animal  substances  can  be  used  by  the 
growing  plant  until  the  bacteria  in  the  soil  cause  them  to 
decay. 

Nitrate  of  soda,  of  which  there  are  great  deposits  in  the 
rainless  regions  of  Chili,  and  sulphate  of  ammonia,  which  is 
a  by-product  of  the  manufacture  of  gas,  are  other  valuable 
sources  of  nitrogen. 

It  has  been  known  for  a  very  long  time  that  a  crop  of  clove* 
seems  to  enrich  the  soil.  As  a  result  of  this  knowledge, 


RELATION  OF  SOIL  TO  PLANTS  325 

most  farmers  after  using  a  field  for  various  crops  for  several 
years  plant  clover  in  it.  In  order  to  understand  this,  we 
must  first  know  that  the  nitrogen  of  the  air  cannot  be  used 
directly  by  plants.  Plants  may  fail  to  grow  because  of 
nitrogen  starvation,  although  the  crevices  in  the  soil  around 
their  roots  and  the  space  around  their  leaves  are  filled  with 
air,  four  fifths  of  which  is  nitrogen.  Clover  and  related 
plants,  such  as  peas,  beans,  alfalfa,  etc.,  have  small  enlarge- 
ments on  their  roots  which  are  not  possessed  by /others. 
These  enlargements  contain  a  certain  kind  of  bacteria 
which  have  the  power  to  convert  some  of  the  ni- 
trogen of  the  air  into  a  form  which  can  be  used  by  the 
plant. 

Several  methods  have  been  discovered  by  which  the 
nitrogen  of  the  air  has  been  made  to  combine  with  some  other 
substance,  forming  a  compound  which  may  be  used  for  plant 
growth.  The  need  for  nitrogen  compounds  during  the  war, 
chiefly  for  making  explosives,  has  caused  large  factories  to  be 
built  for  the  production  of  nitrogen  compounds.  Now  that 
the  need  for  explosives  has  largely  disappeared,  the  prod- 
ucts of  these  factories  may  be  used  to  supply  nitrogen  com- 
pounds needed  for  the  growth  of  plants. 

Problem  4.  How  potassium  and  phosphorus  are  supplied 
to  the  soil.  —  Both  of  these  elements  are  found  in  the  mineral 
part  of  soil.  They  are  usually  in  an  insoluble  form  which 
cannot  be  taken  up  by  plants.  The  action  of  weather  and 
of  the  acids  produced  by  decay  of  vegetable  and  animal 
matter  in  the  soil  change  the  insoluble  potassium  and  phos- 
phorus compounds  into  soluble  'substances  which  can  be 
taken  up  by  plants. 

Decaying  animal  and  plant  matter  not  only  helps  to  make 
the  potassium  and  phosphorus  compounds  already  in  the 


326  GENERAL  SCIENCE 

mineral  part  of  the  soil  usable,  but  as  they  themselves 
contain  compounds  of  these  two  elements  their  addition 
increases  the  supply.  Wood  ashes  spread  upon  the  soil 
improve  the  growth  of  plants  largely  because  of  the  great 
amount  of  potassium  which  they  contain. 

The  chief  source,  however,  of  potassium  fertilizers  has 
been  the  great  deposits  of  Stassfurt,  Germany.  During 
the  war  the  United  States  together  with  all  other  countries 
faced  a  potassium  famine  which  threatened  to  lessen  crop 
production.  At  the  time  the  war  ended,  methods  for  obtain- 
ing potassium  from  rocks  holding  it  in  an  unusable  form 
were  being  perfected.  It  had  also  been  found  that  consider- 
able quantities  could  be  obtained  from  kelp  or  seaweed,  which 
is  very  abundant  on  some  parts  of  the  Pacific  coast.  So,  if 
the  war  had  continued,  we  could  have  had  a  supply  of  potas- 
sium to  meet  all  our  needs. 

One  of  the  sources  of  phosphorus  fertilizers  is  organic 
matter  such  as  slaughter  house  waste  and  fish  scraps ;  bone 
meal  is  especially  valuable  since  a  large  part  of  the  mineral 
material  of  bones  consists  of  a  compound  of  phosphorus. 
Other  important  sources  of  phosphorus  fertilizers  are  phos- 
phate rocks,  and  slag  from  steel  mills.  The  phosphate  rock 
is  found  in  many  of  the  southern  and  western  states.  The 
slag  is  obtained  in  the  process  of  removing  phosphorus  from 
iron  in  the  making  of  steel. 

Problem  5.  How  plants  remove  needed  materials  from 
the  soil. — Review  what  we  have  already  learned  concerning 
how  the  roots  of  plants  are  fitted  to  take  in  water.  Since 
the  dissolved  mineral  substances  in  the  soil  are  taken  in  with 
the  water,  the  adaptations  of  the  roots  for  taking  in  water 
are  also  adaptations  for  taking  in  the  needed  mineral  sub- 
stances. 


RELATION  OF  SOIL   TO  PLANTS  327 

• 

If  the  ashes  of  different  kinds  of  plants  growing  side  by 
side  are  analyzed  by  a  chemist,  it  is  found  that  the  various 
mineral  substances  are  not  present  in  the  same  relative 
amounts.  For  example,  clover  will  contain  many  times  as 
much  lime  or  calcium  as  wheat ;  while  wheat,  on  the  other 
hand,  may  contain  as  much  as  ten  or  fifteen  times  as  much 
silica  as  clover.  Apparently,  the  plant  is  able  to  select  the 
materials  which  it  needs.  This  is  known  as  selective  absorp- 
tion. The  explanation  seems  to  be  that  if  the  living  matter 
of  the  plant  does  not  take  a  certain  kind  of  mineral  sub- 
stance out  of  the  water  which  has  passed  into  the  plant 
through  the  wall  of  the  root  hair,  then  the  sap  or  water  in 
the  root  hair  becomes  saturated  with  that  special  kind  of 
mineral  substance  and  no  more  will  pass  through  the  wall 
of  the  root  hair.  If,  however,  the  plant  uses  a  particular 
mineral  substance,  then  it  is  constantly  being  taken  out  of 
the  sap  and  more  comes  through  the  wall  of  the  root  hair 
to  replace  that  which  has  been  taken  out  by  the  living 
matter. 

Clover,  for  example,  in  its  growth  is  continually  building 
lime  material  into  plant  substance;  and  as  a  result,  more 
lime  comes  through  the  membrane  of  the  root  hair.  Wheat 
does  not  use  nearly  so  much  lime;  and  accordingly,  very 
little  need  come  through  the  root  hair  to  replace  the  amount 
taken  out  by  the  living  matter  of  the  plant. 

Problem  6.  What  plants  do  with  material  taken  from  the 
soil. — You  have  already  learned  how  in  the  green  leaves 
of  the  plant  the  carbon  dioxide  of  the  air  and  the  water  from 
the  soil  are  made  into  starch.  As  a  result  of  the  action  of 
the  living  material  of  the  plant,  the  starch  may  be  made 
into  cell  walls,  and  into  fat  or  oil.  There  are  always  asso- 
ciated with,  the  living  matter  of  the  plant  more  complex 


328  m  GENERAL  SCIENCE 

substances  called  proteins.  These  contain  not  only  carbon, 
hydrogen,  and  oxygen  as  starch  does,  but  also  nitrogen, 
phosphorus,  iron,  etc.,  which  have  been  taken  from  the  soil. 
The  proteins  are  necessary  for  the  growth  of  new  living 
matter. 

Some  of  the  elements,  in  addition  to  being  necessary  con- 
stituents of  living  matter  and  of  the  food  materials  formed 
in  plants,  have  special  duties  to  perform.  Some  seem  to 
neutralize  acids  formed  in  the  plant;  others  are  necessary 
constituents  of  the  coloring  matter  of  plants;  while  still 
others  give  firmness  to  the  woody  substance  of  the  plant. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Use  different  kinds  of  fertilizer  in  your  garden  and  record  the 
results. 

2.  Experiments  to  show  the  water-retaining  power  of  different  kinds 
of  soil. 

REPORTS 

1.  Obtaining  potassium  from  seaweed. 

2.  Records   of   the   amount   of  various  mineral  materials  taken 
from  soil  by  some  of  the  standard  crops. 

REFERENCES  FOR  PROJECT  XXVII 

1.  Soils;    Their  Properties  and  Management,  T.  L.  Lyon.    Mac- 
millan  Company.          ^ 

2.  Agronomy,  Clute.     Ginn  &  Co. 

3.  Story   of  Agriculture  in  the  United  States,   A.   H.  Sanford. 
D.  C.  Heath  &  Co. 

4.  Essentials  of  Agriculture,  H.  W.  Waters.     Ginn  &  Co. 

5.  The  Land  We  Live  In,  O.  W.  Price.     Small,  Maynard  &  Co. 

6.  Earth  and  Sky  Every  Child  Should  Know,  J.  E.  Rogers.     Double- 
day,  Page  &  Co. 

7.  Farm  Science,  W.  J.  Spellman.     World  Book  Company. 

8.  Elementary  Agriculture,  J.  S.  Grim.     Allyn  and  Bacon. 


PROJECT   XXVIII 

HOW  PLANTS  AND   ANIMALS   MAKE   USE   OF  THE 
FOOD   MANUFACTURED  BY  PLANTS 

Problem  1.  Why  must  plants  and  animals  have  food?  — 
Compare  the  growth  of  a  bean  or  pea  seedling,  from  which  the 
seed  leaves  have  been  removed,  with  the  growth  of  one  from 
which  they  have  not  been  removed.  What  is  the  result? 
Since  the  food  for  the  growing  seedling  is  stored  up  in  the 
seed  leaves,  what  is  your  conclusion? 

Your  observations  are  sufficient  without  any  experiments 
to  prove  to  you  that  animals  also  must  have  food.  The 
question  is :  Why  is  food  so  necessary  ? 

We  know  that  animals  and  plants  exert  energy.  Plants 
are  able  to  push  their  roots  through  the  soil  and  against  the 
force  of  gravity  Give  examples  of  this.  Likewise,  animals 
have  the  power  of  movement,  produce  heat,  and  are  able  to 
do  work.  Knowing  that  animals  and  plants  breathe  in 
oxygen  and  breathe  out  carbon  dioxide,  and  that  food  must 
be  taken  in,  what  is  your  conclusion  as  to  what  happens  to 
some  of  the  food  in  the  body?  One  use  of  food,  therefore, 
is  to  act  as  a  fuel  which  when  burned  furnishes  heat,  and 
power  to  do  work. 

Another  use  of  food  is  evident  to  you;  you  weigh  more 
this  year  than  you  did  last  year;  you  say  that  you  have 
grown ;  your  bones  have  become  longer  and  thicker ;  muscles 
are  larger ;  heart  is  a  little  bigger,  etc.  Where  did  the  addi- 
tional material  come  from?  What,  then,  will  you  conclude 

329 


330 


GENERAL   SCIENCE 


is  another  reason  why  plants  and  animals,  and  we,  ourselves, 
must  take  in  food  ? 

In  the  work  of  the  body  there  is  a  certain  amount  of 
wearing  away  of  its  parts.  This  wear  evidently  must  be 
made  good  by  food  being  built  up  into  the  muscles,  nerves, 

and  other  parts  of  the 
body.  State,  now,  the 
three  uses  made  of  food 
by  plants,  animals,  and 
the  human  body. 

Our  next  question 
naturally  will  be :  What 
foods  are  good  for  each 
of  these  purposes  ? 

Problem  2.  What 
foods  are  good  for  fuel, 
and  what  ones  for  growth 
and  repair  ?  —  Consider- 
ation of  the  kinds  of 
food  that  are  eaten 
under  certain  conditions 
may  help  us  to  solve 
this  problem.  People 
living  in  the  Arctic  re- 
gions must  have  food 
which  will  produce  a  great  deal  of  heat.  You  all 
know  that  fat  forms  the  greater  part  of  their  diet.  What 
will  be  your  conclusion,  therefore,  as  to  the  value  of  fat  in 
the  food  ?  Consider  your  own  diet  in  regard  to  the  use  of 
fat.  Do  you  eat  a  greater  quantity  in  winter  or  in  summer  ? 
The  hard  work  of  lumbermen  in  the  northern  woods  is  done 
chiefly  in  winter  (Figure  261).  They  need  food  which  will 


FIGURE  261.  —  LUMBERMEN  AT  WORK. 

Why  do  these  men  need  a  large  amount 

of  energy-producing  food  ? 


USE  OF  THE  FOOD  MANUFACTURED  BY  PLANTS      331 

give  them  heat,  and  the  power  to  do  hard  work.  They  eat 
much  fat  meat,  as  you  would  expect,  but  they  also  eat  a  great 
amount  of  molasses,  large  quantities  of  potatoes,  and  other 
starchy  foods.  This  is  an  indication  of  the  value  of  foods 
which  contain  starch  and  sugar. 

These  observations  concerning  the  use  of  fats,  starch,  and 
sugar  are  in  harmony  with  experiments  which  have  been 
made  as  to  the  value  of  different  food  substances.  Starches 
and  £Ugar,  which  together  are  called  carbohydrates,  and  fats 
because  they  are  common  to  so  many  foods,  are  called  food 
principles  or  nutrients. 

We  have  already  decided  that  foods,  in  addition  to  furnish- 
ing energy,  are  also  necessary  for  growth  and  repair.  For 
this  purpose  it  has  been  found  that  there  must  be  present 
a  food  principle  or  nutrient  called  protein,  and  certain 
mineral  substances.  These  contain  elements  which  are  not 
present  in  fats  and  carbohydrates  but  which  are  necessary 
for  the  building  of  different  parts  of  the  body. 

For  example,  living  matter  contains  nitrogen;  and  as 
protein  is  the  only  nutrient  which  contains  nitrogen,  it  is 
necessary  for  growth  and  repair  of  living  matter.  Foods 
containing  a  large  percentage  of  protein  are  lean  meat,  fish, 
eggs,  milk,  cheese,  beans,  and  peas,  and  to  a  lesser  extent 
cereals  (oats,  wheat,  barley,  and  rye). 

Mineral  matters  are  not  only  necessary  for  the  making  of 
new  living  matter  and  for  the  formation  of  the  bones  of  the 
body,  but  their  presence  is  necessary  for  the  action  of  nerves 
and  muscles,  and  for  the  passing  of  liquids  through  the  walls 
of  the  small  blood  vessels  and  through  other  membranes. 
Iron  has  a  special  duty  in  forming  the  coloring  matter  of  the 
red  blood  corpuscles.  Mineral  materials  are  very  widely 
distributed  among  foods.  Most  natural  foods  contain 


332 


GENERAL  SCIENCE 


considerable  mineral  matter,  so  that  usually  the  ordinary 
diet  contains  a  sufficient  amount.  Milk,  eggs,  lean  meat, 
leafy  vegetables,  fruits,  and  flour  made  from  the  whole  grain 


flnnmn     ^M     mm®     ^^     MM\      •  FUeivaiu9 

Protein  Fat        Carbohydrate*        Ash  Water          •Biooo  Carrie* 

WHITE  BREAD  WHOLE  WHEAT  BREAD 

iter:35.3    Water;38.4 

rotein:9.2     Protein:9.7 


FUEL  VALUE: 


Carbo-  Carbo- 

tes:53.1     hydrates:  49.7 

OAT 
BREAKFAST    FOOD 


121 5  CALORIES  '  Water: 84.5 

PER  POUND 

Protei 

TOASTED  BREAD 

Ash:  0.7 


FUEL   VALUE: 


1140  CALORIES 
PER  POUND 


Fat:  0.5 

rbohydrates:11.5 

CORN  BREAD 


FUEL   VALUE: 


ater:  24.0 
•otein:11.5        Protein77.9 

Carbo-  Carl 

hydrates:  61. 2         hydrates:46.3 

MACARONI 

COOKED 


FUEL  VALUE: 


Carbo- 
hydrates:  15.8 


FuEL 
VALUE: 


41 5  CALORIES 
PER  POUNO 


FIGURE  262.  —  COMPOSITION  OF  BREAD  AND  CEREAL  FOODS. 

are  especially  rich  in  mineral  matter  and  very  nutritious. 

Recent    experiments    have    shown    that    unless   .certain 

chemical  substances  (vitamines)  which  are  found  especially 


USE  OF  THE  FOOD  MANUFACTURED  BY  PLANTS     333 


in  green  vegetables  and  milk  are  present,  normal  growth 
does  not  occur.  Therefore,  it  is  very  important  to  include 
these  in  the  diet. 


onnn 

Protein  Fat        Carbohydrate! 


A»h 


Water 


I    Fuel  Value, 
^Sq.ln.Equals 
1000  Calories 


ONION 


WaU 
Prote'u 

Carbohydrates:  9.9- 
ater:83.0  FUEL  VALUE: 

225  CALORIES 
Protein:!. 6  I I     PER  POUND 

Fat:0.5 
Carbohydrates:  13.5 

il.4 


PARSNIP 

POTATO 

Protein:2.2 


Water.94.5 


Carbohydrates:  18.4     ^Water:78.3 

FUEL   VALUE:  Protein 

Carbohydrates:  3. 

385  CALORIES  PER  POUND 


Ash:1.0 


FIGURE  263.  —  COMPOSITION  OF  SOME  COMMON  VEGETABLES. 

Name  ten  foods  that  are  good  for  supplying  energy. 
Name  five  foods  that  are  good  for  growth  and  repair. 
Problem  3.  How  the  fuel  value  of  foods  is  measured. 


334 


GENERAL  SCIENCE 


Foods  burned  outside  of  the  body  furnish  the  same  amount 
of  energy  as  if  they  were  burned  within  the  body.     The  fuel 


Protein 

COD 

Lean  Fish 


Fat        Carbohydrates         Ash 


Water 


Fuel  Value 
i»Sq. In. Equals 
1000  Calorie* 


FUEL    VALUE: 
.Water:82.6  • 


325  CALORIES 
PER  POUND 
P  rote  in,:]  5. 8 


Wat 


Carbohydrates:  3. 
SMOKED  HERRING 


ate  r:  34.6 
rotein:36..4 

FtTEL    VALUE: 


1355  CALORIES 

PER   POUND 


Ash:T3. 


410    CALORIES 
PER    POUND 

Protein  21.5 


645    CALORIES 
PER   POUND 


FIGURE  264.  —  COMPOSITION  OF  FISH  AND  OYSTERS. 

value  of  carbohydrate,  fat,  and  protein  is  therefore  obtained 
by  burning  known  amounts  of  these  nutrients  in  an  instru- 
ment called  a  calorimeter,  so  constructed  that  all  the  heat 
produced  is  used  to  heat  a  measured  amount  of  water.  The 


USE  OF  THE  FOOD  MANUFACTURED  BY  PLANTS  '  335 


amount  of  heat  necessary  to  warm  a  kilogram  of  water 
one  degree  Centigrade,  is  taken  as  the  unit.    This  unit  is 


mmnnn 

Protein  Fat        Carbohydrates 

WHOLE  EGG 


Ash 


I    Fuel  Value 

Water  ««Sq.ln.Equali 

Water  ••i  000  Calories 

EGG 

WHITE  AND  YOLK 


Protein 

14. 
Fat:  10.5 

Ash:1. 
FUEL  VALUE  OF 

WHOLE  EGG: 


FUEL    VALUE   OF  YOLK: 


700  .CALORIES 
PER  POUND 


CREAM  CHEESE 

Water:  34.: 


1608     CALORIES 
PER  POUND 


/Pr;otein:13.0 

Fat:  0.2 
Ash:0.6 

FUEL   VALUE   OF  WHITE: 

c 

265  CALORIES 
PER  POUND 


COTTAGE  CHEESE 


ltein:25.9Wate!::72-0 


rbo- 
ydrates:  2.4 


in:20.9 


Carbo 
hydrates:  4.3 


FuELVALUE: 
1950    CALORIES  PER  POUMO 


510  CALORIES  PER  POUKD 


FIGURE  265.  —  COMPOSITION  OF  EGGS  AND  CHEESE. 

called  a  calorie.  A  pound  of  pure  starch,  sugar,  or  protein 
will  yield  when  burned  about  1850  calories,  and  a  pound  of 
pure  fat  about  4220  calories. 

It  can  be  seen  that  if  the  amount  of  these  nutrients  in  a 


336 


GENERAL  SCIENCE 


food  are  known,  it  is  very  easy  to  calculate  the  fuel  value 
of  the  food.     The  following  table,  compiled  by  Dr.  Irving 


Protein  Fat         Carbohydrates        Ash 

CORN 

Water:  10.8 

rotein:10.0 


Water 

Water  :1 0.6 
Protein- 12.2 


I  Fuel  Value 
ft  Sq.ln. Equals 
1000  Calories 


WHEAT 


at: 1.7 


FUEL  VALUE; 

BUCKWHEAT 

1800  CALORIES       Protein:  10. 
PER  POUND         f 


Carbohydrates: 73.7 


Water:12.6       |750  CALORIES 
Fat: 2. 2  PER  POUND 


FufLVALUE: 

OAT  .  RICE 

Water:  11.0        1600  CALORIES      Water:12.0- 
Fat:5.0-~$r-Protein:11.8        'ERPOUNO    Protein:' 

m  Carbo-  RYE 

Fat:' 


at:2.0 


Ash:1.0 


FUEL  VALUE; 

HH       hydrates: 73.9  \i£^Ash:1.9 
1720  CALORIES  FUEL  VALUE; 

PER  POUND 


1720  CALORIES 
PER  POUND 


(750  CALORIES 
PER  POUND 


FIGURE  266.  —  COMPOSITION  OF  VARIOUS  GRAINS  USED  FOR  FOOD. 

Fisher  of  Yale,  gives  the  amount  of  each  of  a  number  of 
common  foods  which  will  furnish  100  calories. 

Problem  4.    What  is  the  proper  amount  of  food  ?  —  We 
know  from  experience  that  the  amount  of  food  needed  is 


USE  OF  THE  FOOD  MANUFACTURED  BY  PLANTS     337 

not  the  same  for  all  persons,  and  not  even  the  same  for  one 
person  under  all  circumstances.  Fortunately,  if  we  are  in 
good  health  the  appetite  is  a  fair  guide,  although  if  it  is 
disregarded  and  abused  it  soon  becomes  unreliable.  Eating 
between  meals,  eating  highly  flavored  food,  etc.,  destroys 
the  keenness  of  the  appetite  and  either  undereating  or 
overeating  may  result.  It  is  necessary,  therefore,  to  know 
what  the  body  needs  under  certain  conditions  so  that  the 
appetite  may  not  lead  us  astray. 

Your  own  experiences  will  indicate  to  you  some  of  the 
conditions  that  determine  the  amount  of  food  needed  by 
the  body  as  indicated  by  the  appetite.  Do  you  eat  more 
food  when  you  have  been  spending  the  day  reading  or  when 
you  have  been  playing  outdoors  or  doing  some  active  work? 
Why  do  you  think  this  should  be  true?  Do  you  eat  more 
food  in  summer  or  in  winter?  Explain  the  reason  for  this. 
In  both  of  these  cases  should  the  increase  be  in  energy- 
producing  food  or  in  food  used  for  growth  and  repair? 
Suggest  how  you  think  the  diet  should  be  modified  at  such 
times  ? 

Experiments  have  shown  that  there  is  no  need  for  any 
increase  of  protein,  or  building  material,  in  the  diet  at  times 
when  the  body  is  exerting  more  energy  than  us.ual,  but  that 
the  increase  in  the  amount  of  food  should  be  by  additions  of 
fats  or  carbohydrates. 

Growing  children,  of  course,  should  have  a  slightly  higher 
percentage  of  protein  in  their  food  than  adults.  Explain. 
This  is  well  illustrated  by  the  fact  that  milk,  which  should 
always  be  an  important  part  of  the  food  of  children  and 
which  in  the  earliest  years  constitutes  either  all  or  a  very 
large  part  of  their  diet,  has  a  higher  percentage  of  protein 
than  is  demanded  by  people  who  are  no  longer  growing. 


338 


GENERAL   SCIENCE 


TABLE  OF  100-CALORIE  PORTIONS1 


EDIBLE  PORTIONS 

APPROXIMATE  MEASXTRE 
OF  IOO-CALORIE 
PORTION 

WEIGHT 
IN  OUNCES 
OF  IOO- 
CALORIE 
PORTION 

CALORIES 
DERIVED 

FROM 

PROTEIN 

Almonds             ... 

15  average 

0.5 

12.6 

2  medium 

5.6 

2.5 

Apricots,  fresh  .     .     . 

2  large 

6.1 

7.7 

Asparagus,  cooked  .     . 

2  servings 

7.5 

17.9 

Bacon,     smoked     (un- 

1  thin  slice,  small 

0.6 

6.7 

Ilarce 

3.6 

5.3 

Beans,  baked,  canned 

MOAjf^ 

1  small  serving  (£  cup- 

ful) 

^2.8 

21.5 

string,  canned     .     . 

5  servings 

17.2 

21.5 

lima,  canned  .     .     . 

1  large  saucedish 

4.6 

20.8 

Beef,  corned  .... 

1.2 

21.2 

dried,  salted  and 

smoked  .... 

4  large  slices 

2.0 

67.2 

porterhouse  steak    . 

1  small  steak 

1.3 

32.4 

ribs,  lean    .     .     ... 

1  average  serving 

1.9 

42.3 

ribs,  fat      .... 

0.9 

15.6 

round,  free  from  vis- 

ible fat  .... 

1  generous  serving 

3.1 

80.7 

rump,  lean      .     . 

1.7 

41.0 

rump,  fat  .     .     .     . 

0.9 

17.5 

sirloin  steak  .     . 

1  average  serving 

1.4 

31.0 

Beets,  cooked    .     .     . 

3  servings 

8.9 

23.2 

Brazil  nuts   .     .     .    ;.  . 

3  average  size 

0.5 

10.2 

Bread,  graham  .     .     . 

1  thick  slice 

1.3 

13.5 

toasted     .... 

2  medium  slices 

(baker's) 

1.2 

15.2 

white  homemade 

1  medium  slice 

1.3 

13.8 

average     .... 

1  thick  slice 

1.3 

14.0 

whole  wheat  .     .     . 

1  thick  slice 

1.4 

15.9 

Buckwheat  flour     . 

i  cupful 

1.0 

7.4 

1  The  Approximate  Measure  of  100-Calorie  portions  is  based  in  part  upon 
"Table  of  100  Food  Units,"  compiled  by  Dr.  Irving  Fisher.  The  Weight 
in  Ounces  of  100-Calorie  Portions  and  Calories  derived  from  Protein  are 
based  upon  data  found  on  page  319  of  "  Chemistry  of  Food  and  Nutrition," 
by  Henry  C.  Sherman, 


USE  OF   THE  FOOD   MANUFACTURED  BY  PLANTS     339 


EDIBLE  PORTIONS 

APPROXIMATE  MEASURE 
OF  100-CALORIE 
PORTION 

WEIGHT 

IN  OUNCES 

OF   100- 
CALORIE 

PORTION 

CALORIES 
DERIVED 

FROM 

PROTEIN 

Butter      .     .     .     .     . 

1  tablespoon  (ordinary 

Buttermilk   .     .     .     . 

pat) 
It  cupfuls  (1£  glasses) 
2  servings 

0.5 
9.9 
11.2 

0.5 
33.6 
20.3 

Calf  s-foot  jelly      ... 
Carrots,  fresh    .     .     . 
Cauliflower1      .     .     . 
Celery                            * 

2  medium 

4.1 
7.8 
11.6 
19  1 

19.8 
9.7 
23.6 
23  8 

Celery  soup,  canned  . 
Cheese,  American  pale  l 
American  red  x   . 
'     Cheddar1.     .     .     ,~ 
Cottage     .... 
Neufchatel    .     .     . 

Roquefort1    .     .     ; 

2  servings 
H  cubic  inches 
H  cubic  inches 
li  cubic  inches 
4  cubic  inches  (^  cupful) 
H  cubic  inches  (i  cup- 
ful)  (^  small  pack- 
age) 

li  cubic  inches 

6.6 
0.8 
0.8 
0.8 
3.2 

1.1 
1.0 
0.8 

15.7 
26.5 
26.0 
24.4 
76.1 

23.2 
25.3 
25.4 

Chicken,  broilers    . 
Chocolate     .... 

1  large  serving 
"  generous  half"  square 
2^  tablespoonfuls 

3.3 
0.6 
07 

79.1 
8.3 
17.3 

Cod,  salt      .     .     ...  ;• 
Corn,  green1      .     .   ,. 
Corn  meal    .     .     .    ;  4  •  .. 
Crackers,  graham  .     . 
soda     .     .     .     .     . 

1  side  dish 
2  tablespoonfuls 
3  crackers 
3  crackers 

3.4 
3.6 
.1.0 
0.9 
0.9 

97.5 
11.4 
10.3 
9.6 
9.4 

3  crackers 

0.9 

10.3 

Cranberries  x     .     .     . 
Cream      .     .     .     .     . 

1  cupful  (cooked) 

ij  CUpful 

7.5 
1.8 

3.4 
5.0 

Cucumbers   .     .     .     . 
Dates,  dried      .     .     . 
Doughnuts   .     .     .    •» 
Eggs,  uncooked      .  .. 
Farina      .     .     .     .    •. 

2  large 
4  medium 
£  doughnut 
1£  medium  or  2  small 

20.3 
1.0 
0.8 
2.4 
1.0 

18.4 
2.4 
6.2 
36.4 
12.3 

Figs,  dried    .... 
Flour,  rye     .... 
wheat,  entire 
wheat,  graham  . 
wheat,   average   high 
and  medium   .     . 

1  large 
i?  cupful 
i  cupful 
i  cupful 

\  cupful 

1.1 

1.0 
1.0 
1.0 

1.0 

5.5 

7.9 
15.5 
14.9 

12.8 

1  As  purchased. 


340 


GENERAL   SCIENCE 


EDIBLE  PORTIONS 

APPROXIMATE  MEASURE 
OF  100-CALORIE 
PORTION 

WEIGHT 
IN  OUNCES 
OF  100- 
CALORIE 
PORTION 

CALORIES 
DERIVED 

FROM 

PROTEIN 

4  tablespoonfuls 

1.0 

98:7 

1  large  bunch 

3.7 

5.4 

Haddock 

4.9 

96.3 

Halibut  steaks  .     .     . 
Ham,  fresh,  lean    . 
fresh,  medium     .     . 
smoked,  lean       .     . 
Herring,  whole  . 
Hominy,  uncooked 
Lamb,   chops,    broiled 
leg,  roast  . 
Lard,  refined     .     .     . 
Lemons                         • 

1  average  serving 
1  average  serving 

i  cupful 
1  small  chop 
1  average  serving 
.1  tablespoonful  (scant) 
3  medium 

2.9 
1.5 
1.1 
1.3 

2.5 
1.0 
1.0 
1.8 
0.4 
80 

61.8 
44.0 
19.0 
30.1 
54.6 
9.3 
24.3 
41.0 

(-) 
9.0 

Lettuce    .     .     .     •     • 

50  large  leaves 

20.4 

25.2 

Liver,   veal,  uncooked 
Macaroni,  uncooked  . 
Macaroons    .... 
Mackerel,  uncooked   . 
salt            .... 

2  small  servings 
i  cupful  (4  sticks) 
2 
1  large  serving 

2.9 
1.0 
0.8 
2.5 
1  2 

61.6 
15.0 
6.2 
53.9 
29.5 

Marmalade,  orange     . 
Milk,  condensed, 
sweetened  .     .     . 
skimmed  .... 
whole  .     .     .  •  .     • 

Molasses,  cane  .     .     . 
Muskmelons      .     .     . 
Mutton,  leg  .     .     .     . 
Oatmeal,  uncooked 
Olives,  green     .     .     . 
Onions,  fresh     .     .     . 
Oranges    . 

1  tablespoonful 

ITS  cupfuls 
li  cupfuls  (scant) 
f-  cupful  (generous  half 
glass) 
i  cupful 
£  average  serving 
1  average  serving 
i  cupful 
7  to  10 
2  medium 
1  very  large 

1.0 

1.1 
9.6 

5.1~ 
1.2 
8.9 
1.8 
0.9 
1.2 
7.3 
6  9 

0.7 

10.9 
37.1 

19.1 
3.4 
6.0 
41.2 
16.1 
1.5 
13.2 

fi  9 

Oysters,  canned      .     . 
Parsnips  
Pea  soup,  canned  .     . 
Peaches,  canned     .     . 
fresh     .     .     .     .     • 

5  oysters 
1  large 

1  large  serving 
4  medium 

4.9 
5.4 
6.9 
7.5 

85 

48.6 
9.9 

28.2 
6.0 

A  Q 

10  to  12  (double  kernels) 

06 

18  6 

Peas,  canned     .     .     . 
Peas,  dried,  uncooked 

2  servings 
2  tablespoonfuls 

6.3 
1.0 

25.9 
27.6 

As  purchased. 


USE  OF   THE  FOOD  MANUFACTURED  BY  PLANTS     341 


EDIBLE  PORTIONS 

APPROXIMATE  MEASURE 
OF  IOO-CALORIE 
PORTION 

WEIGHT 
IN  OUNCES 
OF  IOO- 
CALORIE 
PORTION 

CALORIES 
DERIVED 

FROM 

PROTEIN 

Peas,  green  .... 
Pies,  apple    .... 
custard     .     .     ... 

1  generous  serving 
i  piece 
|  piece 
^  piece 

3.5 
1.3 
2.0 
1.4 

28.0 
4.6 
9.4 
56 

\  piece 

1.2 

8.1 

squash       .... 
Pineapples,  fresh    .     . 
canned       .... 
Pork,  chops,   medium 
fat,  salt  l  .    .  .     .     . 
Potatoes,  white, 
uncooked   .     .     . 
sweet,  uncooked 
Prunes,  dried     .     .     . 
Raisins                ... 

£  piece 
5  slices 
1  small  serving 
1  very  small  serving 

1  medium 
£  medium 
3  large 
^  cupful  (packed  solid) 

2.0 
8.2 
2.3 
1.1 
0.5 

4.2 
2.9 
1.2 
i  o 

9.9 
3.7 
1.0 
19.9 
1.0 

10.6 
5.8 
2.8 

Q  0 

Rhubarb,  uncooked    . 
Rice,  uncooked       .     . 
Salmon,  whole  .     .     . 
Shad,  whole       .     .     . 
Shredded  wheat     .     . 
Spinach,  fresh1  .     .     . 

Succotash,  canned 

3%  cupfuls  (scant) 
2  tablespoonfuls 
1  small  serving 
1  average  serving 
1  biscuit 
3  ordinary  servings 
(after  cooking) 
1  average  serving 
13  lumps,  5  teaspoonfuls 
granulated 

15.3 
1.0 
1.7 
2.2 
1.0 

14,7 
3.6 

0.9 

10.4 
9.3 
43.1 
45.9 
11.3 

35.0 
14.7 

(-) 

Tomatoes,  fresh     .     . 
canned      .     .     .     .'•' 
Turkey     

6£  teaspoonfuls  pow- 
dered sugar 
4  average  servings 
If  cupfuls 
1  serving 

15.5 
15.6 
1.2 

15.8 
21.3 

28.7 

2  large  servings  (2  tur- 

Veal, cutlet  .     .     .    > 
fore  quarter  .     .     . 
.    hind  quarter  .     .     . 
Vegetable  soup,  canned 
Walnuts,  California    . 
Wheat,  cracked      ... 
Whitefish      .     .     .   '4   . 
Zwieback      .... 

nips) 

4  whole  nuts 
1  thick  slice 

9.0 
2.3 
2.3 
2.3 

25.9 
0.5 
1.0 
2.4 
0.8 

13.3 
53.6 
52.8 
53.0 
85.3 
10.3 
12.4 
61.4 
9.4 

As  purchased, 


342  GENERAL  SCIENCE 

Another  condition  which  will  affect  the  amount  of  food 
needed  is  the  size  of  the  body.  Other  conditions  being  the 
same,  a  small  person  needs  somewhat  less  food  than  a  larger 
person.  It  has  been  calculated  that  the  number  of  calories 
which  should  be  supplied  by  the  food  when  light  work  is 
being  done  may  be  determined  by  multiplying  the  weight  of 
the  body  by  16.1.  Thus  a  person  weighing  160  pounds  will 
need  sufficient  food  to  furnish  2576  calories.  Of  course,  if 
more  active  muscular  work  is  being  performed,  food  pro- 
ducing a  greater  number  of  calories  is  needed.  A  man  doing 
moderately  active  work  needs  about  3000  calories;  a  farmer 
during  the  busy  season,  as  much  as  4000  calories;  and 
lumbermen,  from  5000  to  9000  calories. 

The  proper  amount  of  protein  in  the  diet  has  been  a  much 
discussed  question.  This  is  of  great  importance,  since  an 
excess  of  protein  in  the  diet  is  harmful  to  the  body.  The 
tendency  of  the  American  people  is  to  eat  rather  more  protein 
than  is  absolutely  necessary,  and  therefore  in  most  cases  the 
diet  would  be  improved  by  cutting  down  the  foods  rich  in 
protein;  for  example,  meats.  About  two  and  one  half 
ounces  or  from  70  to  80  grams  of  protein  a  day  seem  to  be 
sufficient,  according  to  experiments.  It  will  be  found,  how- 
ever, that  our  actual  diet  is.  likely  to  have  nearly  three  and 
one  half  or  four  ounces  or  about  100  grams  of  protein. 

Problem  5.  What  considerations  should  govern  the  plan- 
ning of  our  diet? — It  is  evident  that  our  diet  must  have  the 
proper  fuel  value,  and  contain  the  proper  amount  of  protein. 
Since  there  is  usually  too  much  protein  in  an  unrestricted 
diet,  large  amounts  of  lean  meats  and  other  foods  containing 
a  high  percentage  of  protein  should  be  avoided.  It  would 
be  well  to  calculate  by  the  use  of  the  100-calorie  portion 
tables  given  the  calorie  value  of  your  food  for  a  day.  If  more 


USE  OF  THE  FOOD  MANUFACTURED  BY  PLANTS    343 

than  15  per  cent  of  the  calories  are  from  protein,  then  your 
diet  is  too  rich  in  that.  An  excess  of  fat  or  carbohydrate 
in  the  diet  is  apt  to  cause  an  increase  of  weight  due  to  the 
storing  up  of  excess  fuel  in  the  form  of  fat. 

A  diet  which  contains  the  proper  amount  of  protein,  car- 
bohydrate, and  fat  may,  however,  be  a  very  unsatisfactory 
one.  There  must  be  included  in  it  foods  which  will  supply 
the  minerals  needed  by  the  body,  and  those  minute  sub- 
stances sometimes  called  mtamines,  without  which  normal 
growth  and  repair  does  not  occur.  Vegetables,  whole  grain 
bread  and  cereals,  fruits,  and  milk  are  especially  valuable 
for  their  minerals.  Milk  and  leafy  vegetables  such  as  lettuce 
and  spinach  are  indispensable  in  the  diet.  Fruits  and  coarse 
elements  in  the  food  such  as  the  bran  or  outer  coat  of  wheat 
exert  a  beneficial  effect  upon  the  digestive  organs. 

A  good  diet,  therefore,  will  be  one  which  supplies  the 
proper  amount  of  the  three  nutrients,  and  includes  milk, 
leafy  vegetables,  some  fruit  and  coarse  food  such  as  whole 
wheat  bread,  and  is  so  varied  as  not  to  become  monotonous. 
It  is  presumed,  also,  that  those  parts  of  the  food  which  are 
cooked  have  been  made  both  more  digestible  and  more 
appetizing,  and  that  there  has  been  no  waste  of  their  elements. 

Problem  6.  Why  must  foods  be  digested  ?  —  Consider 
the  condition  in  the  corn  seedling.  Where  is  the  food  stored  ? 
Where  is  growth  going  on,  and  where  is  energy  being  exerted  ? 
The  food  then  must  be  able  to  travel  from  the  seed  to  the 
growing  point.  But  the  young  stem  and  root,  just  as  we 
saw  in  the  older  root  and  in  the  leaves,  are  made  up  of  little 
box-like  structures  (Figure  267)  (cells)  so  that  the  food  in 
reaching  the  point  where  it  is  needed  must  pass  through 
hundreds  of  the  thin  walls  of  these  cells.  The  question  now 
is,  is  the  stored-up  food  in  condition  to  pass  through  these 


344 


GENERAL   SCIENCE 


membranous  walls?    The  following  experiment  will  enable 
you  to  answer  this  question. 

Experiment.- — Break  off  the  bottom  of  a  test  tube  so  that  it  forms 
a  tube  open  at  both  ends.  Over  one  end  of  it  tie  a  piece  of  parch- 
ment paper  or  a  piece  of  the  dried  bladder  of  a  pig  or  other  animal. 
Place  the  tube  with  the  parchment  end  down  in  a  vessel  of  water  in 
which  has  been  stirred  some  starch.  After  about  an  hour  test  the 
water  which  has  come  into  the  tube  through  the  parchment  for  the 
presence  of  starch.  This  test  is  made  by  adding  to  the  water  an 
iodine  solution  which  turns  it  blue  if  starch  is  present.  What  is  the 
result  ?  What  is  your  conclusion  ? 

The  parchment  or  mem- 
brane represents  the  cell  walls 
through  which  the  food  must 
pass.  Evidently  the  starch 
must  be  changed  into  something 
else  or  it  can  be  of  no  value 
to  the  plant.  Since  we  know 
that  it  disappears  from  the 
seed  and  that  energy  is  exerted 
at  the  growing  point,  then  we 
know  that  it  is  changed  into 
something  which  will  pass 
through  the  walls. 

The  protein  and  the  fat  stored 
in  the  seed  are  also  unable  to 
pass  through  membranes  and 
they  too  must  be  changed.  The 
process  by  which  all  of  these 
foods  are  changed  is  called  diges- 
tion. Our  own  foods  must  be 
changed  in  the  same  way ;  starch, 
protein,  and  fats  are  unable  to 


FIGURE  267.  —  CROSS  AND  LON- 
GITUDINAL SECTIONS  OF  A  YOUNG 
ROOT. 

Note  that  the  entire  root  is 
made  up  of  small  divisions 
(cells),  every  one  of  which  is 
surrounded  by  athin  membrane. 


USE  OF  THE  FOOD  MANUFACTURED  BY  PLANTS    345 

• 

get  into  our  blood  until  they  are  changed  into  something 
which  is  able  to  pass  through  membranes. 

Problem  7.  How  can  we  prove  that  nutrients  are 
digested  ?  —  We  have  already  seen  that  starch  cannot  pass 
through  a  membrane  and  that  it  must  be  changed  into  some- 
thing that  will.  Since  sugar  is  very  similar  to  starch  in  its 
chemical  composition,  we  may  suspect  that  starch  may  be 
changed  into  sugar  during  digestion.  But  is  sugar  able  to 
pass  through  a  membrane  ? 

This  may  be  determined  by  trying  the  same  experiment  as 
before,  except  that  a  solution  of  grape  sugar  should  be  sub- 
stituted for  the  mixture  of  starch  and  water.  The  water 
passing  through  the  membrane  may  be  tested  for  grape  sugar 
by  heating  some  of  it  to  which  has  been  added  a  few  drops  of 
Fehling's  solution.  The  presence  of  grape  sugar  is  indicated 
by  a  reddish  orange  or  brick  red  color.  What  is  the  result 
in  this  case  ?  What  is  your  conclusion  ? 

Grind  up  an  unsprouted  corn  grain,  mix  it  with  a  little  water,  and 
test  for  grape  sugar.  Result?  Do  the  same  with  sprouting  corn 
grain.  Result  ?  Conclusion  ? 

Chew  up  a  piece  of  cracker  which  has  been  shown  by  a  test  to  con- 
tain no  grape  sugar.  After  it  has  been  thoroughly  chewed  and  mixed 
with  saliva,  test  again  for  grape  sugar.  Result  ?  Conclusion  ? 

There  is  evidently  something  in  the  sprouting  corn  grain 
and  in  the  saliva  which  has  the  power  to  change  starch  into 
sugar.  A  substance  of  this  kind,  which  by  its  presence  is 
able  to  cause  other  substances  to  change  chemically,  remain- 
ing unchanged  itself,  is  called  an  enzyme.  In  the  corn  grain 
the  enzyme  becomes  active  only  when  the  proper  conditions 
of  temperature  and  moisture  are  present.  There  are  also 
enzymes  that  act  upon  proteins,  and  others  that  act  upon 
fats. 


346 


GENERAL   SCIENCE 


tongue 


pancreas 


Problem  8.  Where  is  food  of  the  human  body  digested? 
—  We  know  that  food  taken  into  the  mouth  passes  down 
tnrough  the  gullet  into  the  stomach,  where  it  remains  for 
several  .hours,  and  then  passes  into  the  small  intestine,  and 
on  into  the  large  intestine.  This  entire  tube  extending  from 
the  mouth  to  the  end  of  the  rectum,  the  last  division  of  the 

large  intestine,  is  called  the 
alimentary  canal.  The  food  is 
forced  along  through  this  tube 
by  means  of  muscles  in  its 
walls. 

After  the  food  has  been  broken 
up  by  the  teeth  and  mixed  with 
saliva  which  acts  to  some  extent 
upon  the  starch,  it  is  worked 
upon  by  enzymes  of  the  gastric 
juice  of  the  stomach  which  act 
chiefly  upon  the  protein  food, 
and  by  a  number  of  enzymes 
from  the  pancreatic  juice  and 
intestinal  juice  which  act  upon 
all  of  the  different  nutrients. 
The  bile,  a  juice  manufactured 
by  the  liver,  is  of  special  use  in  digesting  fat.  As  the  food 
is  digested,  it  is  absorbed  through  the  walls  of  the  alimentary 
canal.  Most  of  the  absorption  occurs  in  the  small 
intestine. 

The  material  which  reaches  the  large  intestine  is  principally 
food  which  could  not  be  digested  and  hence  could  not  be  ab- 
sorbed. If  this  refuse  material  remains  too  long  in  the 
large  intestine,  which  is  the  condition  in  constipation,  bacteria 
act  upon  it  and  produce  soluble  poisons  which  are  absorbed 


epp«ndi 


FIGURE  268.  — FOOD  CANAL 
(ALIMENTARY  CANAL)  OF  MAN. 


USE  OF  THE  FOOD  MANUFACTURED  BY  PLANTS     347 


into  the  blood  through 
the  walls  of  the  large 
intestine  and  give  rise 
to  headaches,  an  in- 
ability to  do  our  best 
mental  and  physical 
work,  and  make  the 
body,  less  able  to  resist 
disease. 

By  the  circulatory 
system  of  the  blood 
(Figure  269)  the  di- 
gested food  is  carried 
to  various  parts  of  the 
body,  where  it  is  used 
for  growth  and  repair 
and  as  a  fuel  for  the 
production  of  energy, 
or  the  excess  of  fuel 
food  is  stored  up  in 
the  form  of  fat. 

The  wastes  which 
are  produced  in  the 
different  parts  of  the 
body  as  a  result  of  oxi- 
dation and  the  activity 
of  the  living  matter, 
are,  in  time,  carried 
away  by  the  circula- 
tory system  to  the 
kidneys,  lungs,  and  skin,  by  which  they  are  taken  out  of 
the  blood. 


FIGURE  269. — ORGANS  OF  CIRCULATION 
OF  MAN. 


348  GENERAL   SCIENCE 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  By  weighing  the  food  used  each  day  for  a  week  and  calculating 
from  tables  showing  percentage  of  nutrients  in  different  foods,  determine 
the  amount  of  each  nutrient  eaten  by  you  during  the  week.     How  does 
the  result  compare  with  the  standard  of  Atwater  or  Chittenden  ? 

2.  Plan  a  bill  of  fare  for  your  family  for  a  week.     Estimate  the 
amount  of  nutrients  and  the  cost.     Suggest  how  the  diet  of  your  family 
might  be  improved  without  any  great  increase  in  cost. 

3.  Perform  experiments  to  show  that  the  gastric  juice  will  digest 
protein. 

4.  Dissect  the  heart  of  a  sheep.     Explain  its  action  in  causing  a 
circulation  of  the  blood. 

REPORTS 

1.  The  value  of  milk  as  a  food. 

2.  The  use  of  fruit  and  fresh  vegetables  as  foods. 

3.  Causes  and  prevention  of  indigestion. 

4.  Causes  and  prevention  of  constipation. 

REFERENCES  FOR  PROJECT  XXVIII 

1.  Feeding  the  Family,  Mary  S.  Rose.     Macmillan  Company. 

2.  The  Story  of  Sugar,  G.  T.  Surface.     D.  Appleton  &  Co. 

3.  Food  and  Household  Management,  Kinne  and  Cooley.     Mac- 
millan Company. 

4.  How  to  Live,  Fisher  and  Fisk.     Funk  &  Wagnalls. 

5.  All    About    Milk.      Metropolitan    Life    Insurance    Company. 
(Free.) 

6.  The  Body  at  Work,  Jewett.     Ginn  &  Co. 

7.  Town  and  City,  Jewett.     Ginn  &  Co. 

8.  The  Story  of  Bread.     International  Harvester  Company,  Chi- 
cago, Illinois. 

9.  Economy  in  the  Buying  and  Preparation  of  Meats,  E.  L.  Wright. 
Wilson  &  Co. 

10.  American  Inventions  and  Inventors,  Mowry.    Silver,  Burdett 
&  Co.      (Foods  cultivated  and  uncultivated.) 


PROJECT  XXIX 
HOW  PLANTS  PRODUCE  SEED 

Problem  1.  Why  plants  produce  seeds  ? — Make  a  list  of 
the  plants  you  know  which  produce  seeds.  In  making  this 
list,  include  grains  and  nuts  as  seeds.  What  is  your  conclu- 
sion concerning  the  number  of  plants  which  produce  seeds? 
If  a  seed  is  placed  in  the  soil  with  the  proper  conditions  of 
moisture  and  temperature,  what  finally  develops  from  it? 
If  a  farmer  wishes  new  wheat  or  grass  or  bean  plants,  what 

does  he  do  ? 
i 

If  you  have  a  garden,  after  the  soil  has  been  prepared  you 
plant  seeds  in  it  which  either  you  or  the  seedsman  have 
obtained  from  plants  grown  the  previous  year.  Weeds  may 
die  as  winter  comes,  but  before  this  happens  they  have  pro- 
duced large  numbers  of  seeds  which  fall  to  the  ground  and 
remain  there  until  the  following  spring.  Considering  these 
and  other  observations  which  you  have  made,  what  is  your 
answer  to  the  question,  why  do  plants  produce  seeds? 
Why  do  you  suppose  plants  produce  so  many  seeds? 

Problem  2.  What  are  the  parts  of  a  seed  ?  —  Soak  a  num- 
ber of  rather  large  seeds  as  peas,  beans,  or  corn.  Examine 
a  bean  seed.  It  will  be  noticed  that  there  is  a  scar  on  one 
edge.  To  understand  the  cause  of  this  scar,  open  a  bean  pod 
and  note  how  the  seeds  are  attached.  While  the  seed  is 
growing,  what  do  you  suppose  passes  through  the  little  stalk 
by  which  the  seed  is  attached  to  the  side  of  the  pod  ?  The 

349 


350 


GENERAL   SCIENCE 


point  of  attachment  of  this  little  stalk  to  the  side  of  the  pod 
is  called  the  placenta.  What  materials  pass  through  the 
placenta  ? 

Remove  the  seed  coat  and  find  two  large  structures  that 
make  up  almost  the  whole  bulk  of  the  seed   (Figure  270). 

These  are  called  seed 
leaves,  and  it  will  be 
noted  that  they  are 
attached  to  a  little 
stalk,  the  pointed  end 
of  which  will  later  de- 
velop into  the  root  of 
the  growing  bean  plant. 
At  the  other  end  of 
the  little  stalk,  and  just 
beyond  where  the  big 
seed  leaves  are  at- 
tached, you  will  see 
two  little  plume-like 
structures  which  at 
first  look  like  the  parts 
of  a  fish's  tail,  but  on 
closer  examination 
prove  to  be  small  leaves.  These  leaves,  with  the  very 
small  stalk  to  which  they  are  attached,  will  develop  into 
the  stem  and  leaves  of  the  plant. 

Altogether  the  bean  seed  is  made  up  of  a  little  plant  called 
an  embryo,  of  which  two  leaves  are  filled  to  such  an  extent 
with  food  material  that  they  have  become  so  thickened  that 
they  no  longer  look  like  leaves.  These  constitute  the  seed 
leaves.  Compare  the  embryo  making  up  the  seed  of  the  bean 
with  a  bean  seedling.  Pick  out  the  corresponding  parts. 


FIGURE  270.  —  SEEPS  OF  BEAN  AND  PEA. 

A  and  C,  little  stem,  lower  end  of  which 
will  develop  into  -the  first  roots.  B,  plu- 
mule, a  bud  which  will  develop  into  the 
stem  and  leaves  of  plant.  A,  B  and  the 
two  large  seed  leaves  constitute  the  em- 
bryo. D,  scar,  the  place  of  attachment 
of  the  little  stalk  within  the  bean  pod.  E, 
micropyle,  a  small  opening. 


HOW  PLANTS  PRODUCE  SEED 


351 


Plumule 


*- — Root 


Examine  a  soaked  pea  seed  and  endeavor  to  find  the  same 
parts  that  you  found  in  the  bean  seed.  In  the  same  way 
compare  the  embryo  of  the  pea  seed  with  a  pea  seedling 
and  note  the  corresponding  parts. 

A  corn  seed  may  be  best  studied  if  it  is  examined  together 
with  one  which  has  begun  to  sprout  (Figure  271).  The  part 
which  corresponds  to  the  root  end  of  the  little  stem  can 
easily  be  seen,  as  in  whatever  position 
the  corn  grain  is  kept  this  root  end 
begins  to  grow  downward.  The  other 
end,  which  begins  to  push  upward  to 
form  the  main  part  of  the  plant,  is 
pointed  and  made  up  of  tightly 
twisted  leaves  in  much  the  same 
way  that  you  can  furl  up  a  piece  of 
paper  leaving  a  sharp  point  at  one 
end. 

The  seed  leaf  (there  is  only  one) 
is  not  at  all  leaf-like  in  appear- 
ance but  is  embedded  in  stored  food  material  which  in 
the  corn  seed  is  outside  of  the  embryo.  The  relation  of 
the  seed  leaf  to  the  stored  food  material  can  best  be  seen  by 
cutting  lengthwise  and  cross  sections  of  soaked  corn  grains, 
and  dipping  the  cut  surfaces  in  an  iodine  solution.  The 
stored  food  material,  since  it  contains  a  very  large  amount 
of  starch,  becomes  colored  a  very  dark  blue ;  while  the  parts 
of  the  embryo  are  colored  very  slightly. 

It  will  thus  be  seen  that  the  corn  seed,  although  apparently 
so  unlike  the  bean  or  pea  seeds,  also  contains  an  embryo,  or 
undeveloped  plant,  which  consists  of  a  seed  leaf  attached  to 
a  stalk,  one  end  of  which  will  develop  into  the  roots,  and  the 
other  end  into  the  stem  and  leaves  of  the  plant. 


FIGURE  271.  — SPROUT- 
ING CORN  GRAIN. 


352  GENERAL   SCIENCE 

Examination  of  other  seeds  will  show  the  same  thing,  so 
that  we  may  conclude  that  the  seed  of  a  plant  always  contains 
an  embryo  or  baby  plant  with  considerable  stored-up  food 
which  may  either  be  in  the  seed  leaves  or  outside  of  the 
embryo. 

Problem  3.  Where  seeds  are  produced.  —  It  is  a  com- 
mon observation  that  seeds  are  produced  in  some  way  by 


FIGURE  272.  —  PEAR,  FROM  BUD  TO  FRUIT  AND  SEED. 

the  flowers  of  a  plant.  It  will  be  well  for  us,  therefore,  to 
examine  a  flower.  An  examination  of  a  typical  flower,  such 
as  a  pear  blossom  or  bean  or  pea  blossom,  will  lead  us  to 
find  the  following  parts  (Figure  272) : 

The  outermost  parts  are  green  leaf-like  structures  called 
sepals.  Together  they  make  a  cup-shaped  formation  around 
the  base  of  the  flower  called  the  calyx.  Just  inside  of  these 
are  the  colored  parts  of  the  flower  called  the  petals.  The 


HOW  PLANTS  PRODUCE  SEED  353 

petals  together  constitute  the  corolla.  Next  there  are  a 
number  of  little  stalks  with  knobs  on  their  tops.  These  are 
the  stamens,  the  stalks  being  called  filaments,  and  the  knobs 
at  the  top,  anthers.  The  anthers  are  little  box-like  structures 
containing  a  powdery  substance  called  pollen. 

The  center  of  the  flower  is  occupied  by  the  pistil,  of  which 
there  are  usually  three  divisions :  an  enlarged  part  at.  the 
base  called  the  ovary,  one  or  more  little  stalks  running  up 
from  this  called  styles,  and  at  the  top  of  the  styles  enlarge- 
ments usually  slightly  rough  and  moist  called  stigmas.  If 
the  ovary  is  cut  through,  there  will  be  found  in  it  small  seed- 
like  structures  which  are  called  ovules.  Very  evidently, 
these  are  the  parts  of  the  flower  which  will  develop  into 
seeds. 

Problem  4.  Do  ovules  always  develop  mto  seeds?  — 
Apparently,  ovules  do  not  necessarily  develop  into  seeds. 
It  will  be  found  by  an  examination  of  a  number  of  pea  or 
bean  pods  that  occasionally  an  ovule  has  not  developed 
into  a  seed.  An  account  of  some  experiments  which  have 
been  performed  many  times  will  help  us  to  understand  why 
ovules  do  not  always  develop  into  seeds.  Stamens  were 
carefully  removed  from  a  flower  before  any  pollen  had 
escaped  from  the  anthers.  The  flower  was  then  covered  with 
a  fine  netting  or  a  paper  bag.  None  of  the  ovules  developed 
into  seeds. 

This  would  indicate  that  the  pollen  is  necessary  for  the 
production  of  the  seeds.  This  conclusion  may  be  confirmed 
as  follows :  A  flower  was  treated  as  the  one  described  above ; 
but  in  this  case  some  pollen  from  another  flower  of  the  same 
kind  was  placed  upon  the  stigmas  of  the  flower  from  which 
the  stamens  had  been  removed.  The  ovules  all  developed 
into  seeds.  What  conclusion  will  you  draw  from  this  result? 


354 


GENERAL  SCIENCE 


Stigma 


Pollen. 
Grain 

Tube 


•Nucleus 


Loose  Tissue 
•of  Style 


Problem  5.  How  the  pollen  grain  influences  the  de- 
velopment of  the  ovule  into  the  seed.  —  It  has  been  found 
that  each  pollen  grain  resting  upon  the  surface  of  the  stigma 
grows  out  into  a  tube  which  pushes  its  way  down  through 
the  style  until  it  reaches  the  ovary  (Figure  273).  The  pollen 

tube  now  grows  through  a  small 
opening  (micropyle)  on  the  side  of 
the  ovule  (Figure  274).  Some  of 
the  living  material  (sperm  cell) 
of  the  pollen  grain,  containing  a 
denser  portion,  the  nucleus,  passes 
down  through  the  tube. 

After  the  tube  has  penetrated 
into  the  ovule  through  the  micro- 
pyle, the  end  of  the  tube  disap- 
pears and  the  nucleus  of  the  pollen 
(sperm  cell  nucleus)  combines  with 
the  nucleus  of  a  little  bit  of  living 
matter  in  the  ovule  called  the  egg  cell.  The  egg  cell,  which 
is  now  composed  of  living  material  from  the  pollen  grain 
in  addition  to  its  own  original  living  material,  grows  and 
divides  into  two,  then  four,  eight,  and  finally  thousands 
of  little  masses  of  living  matter  (cells)  which  arrange 
themselves  to  form  the  parts  of  the  embryo  or  baby  plant. 

The  egg  cell,  which  is  composed  of  living  material  from 
these  two  sources,  is  called  a  fertilized  egg  cell ;  and  the 
union  of  the  sperm  cell  nucleus  with  the  egg  cell  nucleus  is 
called  the  process  of  fertilization.  Unless  this  process  of 
fertilization  occurs,  the  egg  cell  will  not  grow  and  divide, 
but  will  finally  wither  and  die. 

In  all  living  things  except  the  very  lowest  animals  and 
plants,  this  general  process  of  the  union  of  two  masses  of 


FIGURE  273.  —  GROWTH 
OF  POLLEN  TUBES  DOWN 
THROUGH  THE  STYLE. 


HOW  PLANTS  PRODUCE  SEED 


355 


living  matter  precedes  the  development  of  an  egg  into  a  new 
plant  or  animal. 

Problem  6.  Does  it  make  any  difference  whether  the 
pollen  comes  from  the  same  flower  or  a  different  one  ?  — 
It  is  clear  that  if  seeds 
are  produced  by  a  plant 
the  pollen  must  in  some 
way  pass  from  the 
anther  to  the  stigma. 
This  would  seem  very 
easy,  as  the  flowers  of 
most  plants  have  both 
stamens  and  pistils. 
Experiments,  however, 
by  the  great  English 
scientist,  Charles  Dar- 
win, have  shown  that 
in  many  plants  cross- 
pollination  (transfer  of 
pollen  from  an  anther 
of  one  flower  to  the 
stigma  of  another  flower 

of  the  same  kind)  gave     Coat  of  ovule ;    D,  inner  coat  of  ovule ; 
much  more  satisfactory     E>  embryo  sac ;    F,  sperm  cell  nucleus ; 

G,  egg  cell  nucleus. 

results  than  if  the  pol- 
len that  fell  upon  the  stigma  came  from  the  anther  of  the 
same  flower  (self-pollination).  He  found  in  some  cases  of 
self-pollination  that  a  smaller  number  of  seeds  were  pro- 
duced ;  that  the  seeds  were  frequently  smaller  and  that 
poorer  plants  *  developed  from  the  seeds.  Naturally  the 
question  arises  as  to  how  self-pollination  is  prevented,  and 
how  cross-pollination  is  encouraged. 


FIGURE  274.  —  POLLEN  TUBE  ENTERING 

OVULE. 
A,  pollen  tube ;  B,  micropyle ;    C,  outer 


356 


GENERAL   SCIENCE 


Problem  7.  How  self-pollination  is  prevented.  —  Some 
plants,  like  the  willow  and  the  cottonwood  or  poplar,  have 
flowers  containing  only  stamens  on  one  plant  and  flowers 
having  only  pistils  on  another  plant.  In  these  cases  self-pol- 
lination is  impossible.  Other  plants,  among  which  are  corn 
(Figures  275  and  276)  and  many  of  our  common  trees  as  ash, 
chestnut  (Figure  277),  oak  (Figure  278),  maple,  hickory, 

pines,  etc,,  have  stamens 
and  pistils  in  different 
flowers  but  on  the  same 
plant. 

In  corn,  for  example, 
the  tassel  (Figure  276) 
at  the  top  of  the  corn 
plant  is  a  collection  of 
staminate  flowers';  while 
the  silks  (Figure  275)  of 
the  ear  of  corn,  down 
along  the  stalk,  are 
stigmas  and  styles,  and 
the  corn  grains  are  ovaries 
of  the  pistillate  flowers. 
Even  in  this  kind  of 
plants  better  results 

occur  when  the  pollen  is  carried  from  the  anthers  of  another 
plant.  A  solitary  cornstalk  usually  has  on  it  very  poorly 
developed  ears  of  corn. 

In  many  plants  the  stamens  ripen  and  the  pollen  escapes 
from  the  anthers  before  the  stigmas  in  the  same  flower  are 
ready  to  receive  it.  In  some  plants  the  reverse  is  true,  the 
stigma  being  ready  to  receive  pollen  before  the  pollen  in  that 
plant  is  mature. 


FIGURE  275.  —  PISTILLATE  FLOWERS  OF 
CORN. 

Each  silk  (style  and  stigma)  is  at- 
tached at  its  base  to  the  young  corn 
grain  (ovary). 


HOW  PLANTS  PRODUCE  SEED 


357 


Experiments  have  shown  that  in  some  flowers  if  the  pollen 
from  the  same  flower  and  pollen  from  a  different  flower  of 
the  same  kind  are  placed  side  by  side  upon  the  stigma,  the 
pollen  tube  of  the  pollen  of  the  other  flower  will  grow  more 
rapidly  than  the  tube  of  the  pollen  of  the  same  flower. 

Problem  8.  How  pollen 
is  carried  from  one  flower 
to  another.  —  If  a  branch  of 
a  pine  or  oak  tree  or  a  piece 
of  ragweed  or  a  corn  tassel 
is  shaken  slightly  at  the  time 
the  pollen  is  ripe,  the  pollen, 
in  the  form  of  a  light,  dry  dust, 
will  fall  out  in  great  quanti- 
ties. How  do  you  suppose 
pollen  of  these  flowers  may 
be  carried  from  one  flower 
to  another?  Explain  the 
reason  for  the  enormous 
quantity  of  pollen  produced. 
The  stigmas  of  flowers  pol- 
linated in  this  way  are  fre- 
quently very  much  enlarged 
and  branched  so  as  to  expose 
a  large  surface.  What  is  the 
advantage  of  this?  These 
flowers  that  are  pollinated  by  the  wind  do  not  correspond 
in  their  appearance  to  our  idea  of  flowers.  They  are  usually 
greenish  and  inconspicuous  with  no  odor  or  bright  colors. 

Many  flowers  have  pollen  which  is  not  so  dry  and  light  as 
that  of  the  flowers  we  have  been  considering.  They  evi- 
dently cannot  have  pollen  carried  to  any  extent  by  the  wind. 


FIGURE  276  —  CORN  TASSEL  MADE 
UP  OF  STAMINATE  FLOWERS. 


358 


GENERAL   SCIENCE 


These  are  our  familiar 
flowers  (Figures  279  and 
280),  of  various  colors 
and  frequently  having 
more  or  less  odor.  You 
will  recall  that  you  have 
often  seen  insects,  es- 
pecially bees  and  but- 
terflies, visiting  them. 
The  insects  are  seeking 
the  sweet  material,  nec- 
tar, which  is  down  in 
the  interior  of  the  flowers. 
By  pulling  out  the  little 
flowers  from  a  head  of 
red  clover,  and  touching 
their  bases  with  the 
tongue,  you  can  taste 
the  nectar.  Examination  of  the  head  of  a  butterfly  and 


FIGURE  277.  —  STAMINATE  FLOWERS  OF 
CHESTNUT. 


FIGURE  278.  —  FLOWERS  OF  OAK. 


HOW  PLANTS  PRODUCE  SEED  359 

the  legs  and  body  of  a  bee  will  show  you  that  they  are  cov- 
ered with  hairs.  Explain  now  how  you  believe  these  flowers 
are  pollinated. 

The  irregular  shapes  of  flowers  are  in  general  associated 
with  making  more  certain  that  the  proper  kinds  of  insects 


FIGURE  279.  —  FLOWERS  OF  HORSECHESTNUT. 

will  visit  them ;  and  the  stamens  and  pistils  are  so  arranged 
that  the  insect  is  quite  certain  to  rub  against  them  to  receive 
pollen  from  one  flower,  and  then  to  rub  the  pollen  off  on  the 
stigma  of  the  next  flower  visited. 


360 


GENERAL  SCIENCE 


Some  flowers  have  their  pollen  carried  by  water ;  and  in 
some  cases  humming  birds  act  as  the  carriers ;  but  the  great 
majority  of  flowers  are  pollinated  either  by  wind  or  by  in- 
sects. Insect-pollinated  flowers  have  much  less  pollen  than 
wind-pollinated  flowers.  Explain. 


FIGURE  280.  —  CHERRY  BLOSSOMS. 

Suggest  any  advantage  of  the  grouping  into  clusters  of  these  small 
white  flowers. 

Nearly  all  of  the  flowers  that  bloom  at  night  are  white 
or  yellow.  What  reason  can  you  give  for  this?  Flowers 
have  various  means  of  excluding  small  crawling  insects  like 
ants.  Of  what  advantage  is  this  to  the  plant  ? 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Make  a  collection  of  seeds  and  give  a  brief  statement  of  the  eco- 
nomic value  of  each  seed. 

2.  Germinate  ten  different  seeds.     Make  sketches  of  several  stages 
of  the  development  of  each. 


HOW  PLANTS  PRODUCE  SEED  361 

3.  Examine  ten  different  flowers.     Make  sketches  of  the  essential 
organs  of  each. 

4.  Cross-pollinate  a  number  of  flowers  of  a  plant. 

5.  Grow  pollen  tubes  from  the  pollen  of  several  kinds  of  flowers  in 
sugar  solutions  of  different  densities. 

6.  Observe  a  bed  of  flowers  for  a  considerable  time  to  find  out  the 
kinds  and  numbers  of  insects  that  visit  the  flowers.     Catch  some  of  the 
insects  and  examine  them  to  find  whether  they  are  carrying  pollen  and 
how  well  fitted  they  are  for  this  purpose.     Also  determine  whether  the 
flowers  are  fitted  in  any  special  way  to  profit  by  the  visits  of  the  insects. 

7.  Make  a  collection  of  the  flowers  of  a  number  of  common  trees. 

8.  Collect  frogs'  eggs  and  describe  the  changes  which  they  undergo 
when  kept  in  an  aquarium. 

REPORTS 

1.  Describe  the  methods  of  cross-pollination. 

2.  Describe  special  devices  in  several  flowers  to  prevent  self-pollina- 
tion and  to  bring  about  cross-pollination. 

REFERENCES  FOR  PROJECT  XXIX 

1.  Farmers'  Bulletin  154,  The  Home  Fruit  Garden;  218,  The  School 
Garden ;    255,  The  Home  Vegetable  Garden ;    408,  School  Exercises  in 
Plant  Production. 

2.  The  Home  Vegetable  Garden,  Adolph  Kruhm.     Orange  Judd 
Company. 

3.  Outline  Studies  on  School  Garden,  Home  Garden,  and  Vegetable 
and   Growing  Projects,   Kern.     Division  of  Agricultural  Education, 
University  of  California. 

4.  Wild  Flowers  Every  Child  Should  Know,  Stack.     Doubleday, 
Page  &  Co. 


PROJECT   XXX 

HOW  BETTER  PLANTS   AND   ANIMALS   ARE 
PRODUCED 

Problem  1.  Have  we  evidence  of  improvement  of  plants 
and  animals  during  past  generations  ?  —  Of  course  we  mean 
by  improvement,  making  these  plants  and  animals  better 
fitted  to  meet  our  needs.  The  history  of  some  of  our  domes- 
ticated animals  and  plants  runs  back  to  the  point  where 
our  knowledge  of  the  history  of  man  begins,  so  that  it  is 
impossible  to  trace  them  directly  from  their  wild  ancestors. 
They  may,  however,  be  compared  in  some  cases  with  wild 
plants  and  animals  which  apparently  are  similar  to  these 
unknown  ancestors.  Wheat,  oats,  rye,  barley,  etc.,  have 
evidently  been  derived  from  wild  grasses,  from  which  they 
now  differ  chiefly  in  the  amount  of  food  material  stored  in 
the  grain  or  seed. 

Chickens  have  changed  much  from  the  Asiatic  bird  which 
is  thought  to  be  most  nearly  like  the  one  from  which  they 
have  descended.  Dogs  have  become  quite  unlike  their  wild 
ancestors,  apparently  wolves  and  coyotes  or  the  close  rela- 
tives of  these.  Turkeys,  which  have  become  domesticated 
in  relatively  recent  times,  have  already  begun  to  be  changed 
in  some  respects  from  the  wild  turkeys  which  were  found  in 
the  American  woods  by  the  early  settlers. 

The  most  striking  effect  of  the  influence  of  domestication 
in  causing  improvement  in  plants  is  shown  by  those  plants 
which  are  native  to  America  and  whose  whole  histories  are 

362 


HOW  BETTER  PLANTS  AND  ANIMALS  ARE  PRODUCED    363 

known.  The  Indian  corn,  which  explorers  found  the  Ameri- 
can Indians  cultivating  in  a  very  crude  way,  would  hardly 
be  recognized  as  being  related  to  the  large-grained,  full- 
eared  corn  whose  crop  in  1920  was  worth  over  $4,000,000,000. 

The  potatoes  found  by  these  early  explorers  were  about 
the  size  of  marbles.  During  the  few  hundreds  of  years  since 
they  have  been  cultivated  by  civilized  man,  both  quality 
and  size  have  been  greatly  improved.  In  1920  the  average 
yield  per  acre  was  over  100  bushels;  some  areas  yielding 
300  to  400  bushels  per  acre. 

Not  only  has  there  been  an  improvement  under  domesti- 
cation of  the  plants  and  animals  mentioned  above,  but  the 
same  is  true  to  a  greater  or  less  extent  of  all  plants  and 
animals  for  which  we  have  use.  The  question  that  arises 
in  our  minds  is,  how  has  this  improvement  been  brought 
about,  and  how  may  we  continue  the  process  ?  . 

Problem  2.  How  plants  and  animals  may  be  improved 
by  selection.  —  From  the  very  earliest  times  selection  has 
been  a  factor  in  producing  better  animals  and  plants.  Se- 
lection has  depended  upon  two  facts  with  which  we  are  all 
familiar :  first,  that  no  two  plants  or  animals  are  exactly 
alike;  and  second,  that  a  plant  or  animal  tends  to  be  like 
its  parents.  In  a  classroom,  for  example,  there  are  no  two 
pupils  exactly  alike.  This  is  also  true  if  we  consider  all  the 
people  in  the  whole  world.  Likewise,  you  will  find  that  no 
two  bean  or  wheat  plants  or  apple  trees  or  horses  are  exactly 
alike  (Figure  281).  This  we  call  variation. 

On  the  other  hand,  each  pupil  in  the  class  resembles  his 
parents  or  grandparents  in  many  respects.  It  may  be  in 
the  shape  of  the  nose  or  face,  coloring,  tone  of  voice,  size, 
mental  traits,  etc.  The  same  is  true  of  every  plant  and 
animal.  Chickens  never  come  from  duck  eggs,  or  chestnuts 


364 


GENERAL  SCIENCE 


from  cherry  trees.  Every  plant  or  animal  resembles  its 
parents  in  hundreds  of  ways.  This  law  of  resemblance  is 
called  heredity;  and  we  say  that  a  person  inherits  a  good  dis- 
position, black  eyes,  etc.,  from  his  antecedents.  The  farmer, 
who  each  year  selects  the  best  corn  or  wheat  grains  for  seed, 


FIGURE  281. — VARIATION. 

Variation  in  the  size  and  shape  of  timothy  heads  in  the  same  kind 
of-  timothy. 

will  keep  his  crops  up  to  the  highest  grade.  He  may  select 
for  any  special  characteristic;  size  of  ear,  rapid  growth, 
large  or  small  amount  of  starch,  protein,  or  oil. 

Problem  3.  How  more  rapid  improvement  may  be 
brought  about.  —  Greater  variation  may  be  brought  about 
by  pollinating  flowers  by  hand.  By  this  means  also,  a 
variety  of  plant  or  fruit  possessing  certain  desirable  char- 
acteristics may  be  obtained  rather  quickly.  For  example, 


HOW  BETTER  ANIMALS  AND  PLANTS  ARE  PRODUCED    365 


edible  oranges  cannot  be  produced  in  a  region  where  frosts 
are  likely  to  occur.  There  is,  however,  a  species  of  orange 
tree  having  a  bitter,  uneatable 
fruit  which  is  very  hardy  and 
will  grow  much  farther  north 
than  the  sweet  orange. 

In  1896  and  1897,  plant 
breeders  of  the  United  States 
Department  of  Agriculture  at- 
tempted to  produce  an  edible 
orange  which  would  grow  much 
farther  north.  This  was  done  in 
the  following  way.  Pollen  from 
the  flowers  of  the  bitter  orange 
was  placed  on  the  stigmas  of 
flowers  of  the  sweet  orange  and 
vice  versa.  This  was  done  for 
thousands  of  flowers,  and  is  called 
hybridizing. 

There  was  great  variation  in 
the  plants  that  developed  from 
the  seeds  of  these  flowers.  The 
young  plants  were  grown  where 
they  would  be  exposed  to  con- 
siderable cold.  Many  of  them 
could  not  withstand  the  low  temperature  and  died.  Others 
which  showed  good  healthy  growth  in  spite  of  the  cold 
were  grafted  l  upon  orange  trees.  Out  of  the  thousands 

1  That  is,  the  end  of  the  branch  of  an  orange  tree  was  cut  off  and  in 
a  slit  cut  in  the  end  of  it  was  placed  a  one-year-old  seedling  plant  (the 
graft) .  The  important  thing  about  this  is  that  the  fruit  borne  on  the 
grafted  part  is  the  same  as  though  the  twig  had  grown  from  its  own 
roots. 


FIGURE  282. — TONGUE 
GRAFTING. 

In  all  forms  of  plant  graft- 
ing, it  is  essential  that  the 
actively  growing  layer 
(cambium)  situated  be- 
tween the  bark  and  the 
wood  of  the  graft  be  held 
in  contact  with  the  cam- 
bium layer  of  the  plant  to 
which  the  graft  is  attached. 


366 


GENERAL   SCIENCE 


of  grafts  made,  only 
three  produced  fruit 
that  was  of  value.  The 
flavor  of  these  was  good 
and  they  possessed  the 
advantage  of  being  able 
to  live  two  to  four  hun- 
dred miles  north  of 
where  the  ordinary 
sweet  orange  was  able 
to  exist.  These  varie- 
ties were  propagated  in 

FIGURE  283.  — CLEFT  GRAFTING.  turn     by    further    graft- 

ing. 

In  plants  that  can  be  propagated  by  cuttings,  as  roses, 
carnations,  geraniums,  etc. ;  by  roots,  rootstocks,  or  tubers, 


FIGURE  284.  —  BUDDING,  A  FORM  OF  GRAFTING. 
The  four  successive  steps  are  shown  left  to  right. 


HOW  BETTER  ANIMALS  AND  PLANTS  ARE  PRODUCED    367  ' 

as  potatoes,  gladioli,  etc. ;  or  by  grafting,  as  fruit  trees, 
favorable  variations  obtained  by  hybridizing  may  be  readily 
retained.  In  plants,  however,  that  are  propagated  only  by 
seed,  as  cotton,  corn,  wheat,  most  vegetables,  etc.,  a  process 
of  rigorous  selection  must  follow.  After  four  to  six  genera- 
tions the  plants  will  "  come  true  to  seed  "  fairly  well,  but 
the  process  of  selection  must  continue  every  year  or  the 
desirable  characteristics  will  disappear. 

Very  striking  results  have  been  obtained  by  plant  and 
animal  breeders  through  the  use  of  selection  and  hybridiz- 
ing. Luther  Burbank  especially  has  developed  some  very 
interesting  plants,  such  as  the  white  blackberry  and  spine- 
less cactus. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  From  a  corn  or  wheat  crop,  etc.,  make  a  selection  of  seed  to  bring 
about  an  improvement  along  some  definite  line  in  future  crops. 

2.  Graft  the  twig  of  one  kind  of  apple  tree  upon  the  limb  of 
another. 

3.  Propagate  a  number  of  different  kinds  of  plants  by  cuttings. 

REPORTS 

1.  Improvement  of  the  corn  crop. 

2.  Improvement  of  the  wheat  crop. 

3.  Reports  on  various  achievements  of  Luther  Burbank. 

4.  The  work  of  the  U.  S.  Bureau  of  Agriculture  in  developing  new 
species  of  animals  and  plants. 

5.  Give  a  brief  account  of  the  work  of  Charles  Darwin. 

6.  Give  a  brief  account  of  the  work  of  Gregor  Mendel. 

REFERENCES  FOR  PROJECT  xxx 

1.  New  Creations  in  Plant  Life :  Life  and  Work  of  Luther  Burbank, 
W.  S.  Harwood.  Grosset  &  Dunlap,  1907. 


368  GENERAL  SCIENCE 

2.  Evolution    of  Our  Native  Fruits,  L.   H.  Bailey.     Macmillan 
Company. 

3.  The  Story  of  a  Grain  of  Wheat,  W.  C.  Edgar.     D.  Appleton  &  Co. 

4.  Corn  Plants,  Their  Uses  and  Ways  of  Life,  F.  L.  Sargent.     Hough- 
ton  Mifflin  Company. 

5.  Plant  Production,  Moore  and  Halligan.  American  Book  Company. 


PROJECT   XXXI 


INSECT   ENEMIES    OF   PLANTS 

Problem    1.     How   insects    are    injurious   to   plants.  — 

Most  of  you  know  some  of  the  ways  in  which  insects  are 

injurious  to  plants. 
You  have  seen  rose 
bushes,  currant  bushes, 
or  even  whole  trees 
stripped  of  their  leaves 
by  little  worm-like  ani- 
mals (Figures  285  and 
291).  If  you  have  had 
a  garden  or  have  been 
in  the  country  in  sum- 
mer you  have  seen 
potato  bugs,  or  more 
accurately,  potato 
beetles  (Figure  286). 

You  may  have  seen 
a  little  heap  of  sawdust 
at  the  foot  of  a  plum, 


GYPSY 


FIGURE  285.  —  LIFE  HISTORY  OF 
MOTH. 

One  of  the  insects  most  injurious  to 
foliage  of  shade  and  forest  trees.  Common 
in  the  New  England  States. 


peach  or  cherry  tree 
which  led  you  to  find  a 
grub,  a  worm-like  animal,  eating  a  tunnel  in  the  wood  under 
the  bark  (Figure  287),  which  if  not  detected  would  have  killed 
the  tree  (Figure  288).  You  may  have  seen  lumber  which  has 
been  meide  useless  by  wormholes  made  by  grubs,  a  young 


370 


GENERAL   SCIENCE 


stage  of  beetles ;  or  you  have  had  the  leaves  of  plants  in  your 
flower  or  vegetable  garden  eaten  by  grasshoppers.  If  you 
have  been  in  an  orchard  which  has  not  been  well  cared  for, 
you  have  found  that  practically  every  apple  was  "  wormy  " 
(Figure  289).  The  "worm"  is 
the  young  stage  of  a  small  moth 
which  flies  at  night. 


FIGURE  286.  —  POTATO  BEETLE. 


FIGURE  287.  —  PEACH-TREE 
BORER. 


These  are  only  a  few  of  the  enormous  number  of  ways  in 
which  insects  harm  crops,  fruit,  and  forests  by  eating  them. 
Give  other  examples  seen  by  you. 

Another  group  of  injurious  insects  is  represented  by  the 
plant  lice  which  you  sometimes  see  on  house  plants.  They 
do  much  damage  to  plants  in  general.  And  there  are  the 
scale  insects  (Figure  290)  which  at  various  times  have 
ruined  all  of  the  fruit  trees  in  certain  parts  of  the  country. 


INSECT  ENEMIES  OF  PLANTS 


371 


FIGURE  288.  —  GROUP  OF  DYING  LOCUST  TREES. 
Effect  of  borers  and  leaf -miners. 

The  squash  bug  is  another  example  of  this  group  of  in- 
sects  which   does   harm    by    sucking   out    the    juices    of 


FIGURE  289.  —  WORM  IN  APPLE,  LARVA  OF  CODLING  MOTH. 


372 


GENERAL   SCIENCE 


plants.     The  bedbug,  of  unsavory  reputation,  is  a  close 
relative. 

It  has  been  estimated  by  the  Chief  of  the  Bureau  of  Ento- 
mology of  the  United  States  Department  of  Agriculture 
that  the  damage  done  in  one  year  in  this  country  by  insects 
is  as  follows:  Farm  crops  —  cereals,  $430,000,000;  hay, 
$116,000,000;  cotton,  $141,000,000;  tobacco,  $17,000,000; 


FIGURE  290.  —  SCALE  INSECTS  ON  A  FERN  LEAF. 


vegetables,  $200,000,000;  sugar,  $8,000,000;  fruits,  $141,- 
000,000 ;  other  crops  about  $55,000,000 ;  making  a  total  of 
over  $1,100,000,000  damage  done  to  farm  crops. 

In  addition,  forests  and  forest  products  are  estimated  to 
have  suffered  a  damage  of  $100,000,000 ;  products  in  storage, 
$100,000,000;  insect-borne  diseases  of  man  have  caused  a 
loss  of  $150,000,000 ;  domestic  animals  have  been  damaged 
to  the  extent  of  $100,000,000 ;  making  a  grand  total  of  more 
than  $1,500,000,000. 

The  question  is,  how  can  this  great  loss  be  lessened? 

Problem  2.    How  injurious  insects  may  be  destroyed.  — 


INSECT  ENEMIES  OF  PLANTS 


373 


What  do  you  think  would  be  the  best  method  of  destroying 
insects  that  eat  the  leaves  of  plants?  The  usual  way  is  to 
spray  the  tree  (Figure  292)  with  a  poisonous  mixture.  Paris 
green  mixed  with  lime  and  water  is  frequently  used.  Ar- 


FIGURE  291. — TENT  CATERPILLARS. 
Nest  and  larvae  of  apple  tree  tent  caterpillar  in  wild  cherry  tree. 

senate  of  lead  is  less  apt  to  injure  the  leaves  and  is  replacing 
Paris  green  to  a  great  extent.  To  prevent  apples  from  be- 
coming wormy,  it  is  necessary  to  spray  the  tree  just  as  the 
petals  fall  from  the  blossom  and  while  the  calyx  is  still  open. 
This  is  because  the  moth  lays  eggs  in  the  blossom  and  the 


374 


GENERAL  SCIENCE 


poison  must  get  into  the  cup  formed  by  the  calyx  before 
the  little  larva,  or  "  worm,"  has  a  chance  to  eat  its  way 
into  the  fruit. 

Of  course  insects  that  live  by  sucking  juices  from  plants 


FIGURE  292.  —  A   MODERN  SPRAYING  OUTFIT. 

are  not  affected  by  poisonous  sprays.  They  are  usually 
killed  by  being  suffocated  in  some  way.  Dry  insect  powder 
may  be  sprayed  over  the  plant  by  bellows.  This  clogs  up 
the  breathing  holes  along  the  body  of  the  insect.  A  spray 


INSECT  ENEMIES  OF  PLANTS 


375 


made  of  kerosene,  soap,  and  water,  another  made  of  whale 
oil  soap,  and  still  another  made  by  pouring  hot  water  over 
tobacco  stems,  have  been  found  to  be  effective  in  killing  these 
sucking  insects.  In  greenhouses  and  cold  frames  which 
can  be  tightly  closed,  tobacco  smoke  is  valuable  for  killing 
plant  lice. 


FIGURE  293. — A  BENEFICIAL  BEETLE. 
Caterpillar  of  gypsy  moth  attacked  by  Calosoma  beetle. 

Problem  3.  How  the  number  of  injurious  insects  is 
reduced  by  natural  means.  —  Man's  fight  against  injurious 
insects  might  be  a  losing  one  if  he  were  not  assisted  by  the 
many  animals  that  prey  upon  insects.  The  big  dragon 
flies  which  you  see  soaring  in  the  air,  reminding  you  of  minia- 
ture airplanes,  are  on  the  lookout  for  flying  insects,  of  which 
they  devour  an  enormous  number.  The  immature  stage 
(larva)  of  the  dragon  fly,  living  in  ponds,  have  also  as  their 
one  occupation  the  destruction  of  the  young  stages  of  other 
insects. 

Ladybird  beetles  (Figure  294),  commonly  called  "  lady- 
bugs/'  those  small  round  beetles  which  most  of  us  know, 
are  very  helpful  in  keeping  down  the  increase  of  plant  lice 
and  scales  (Figure  295).  A  number  of  years  ago  a  species  of 
the  ladybird  beetle  saved  the  orange  industry  of  California. 


376 


GENERAL  SCIENCE 


The  orange  groves- were  threatened  with  destruction  by  a 
scale  insect  introduced  from  Australia.  As  its  spread  could 
not  be  stopped  by  the  ordinary  methods  of  fighting  insects, 
an  expert  in  the  study  of  insects  was  sent  to  Australia  to 
find  if  the  scale  had  any  natural  enemy.  It  was  found  that 
a  certain  kind  of  ladybird  beetle  fed  upon  them  and  thus 


FIGURE  294.  —  LADYBIRD  BEETLE. 

kept  them  in  check.  Beetles  were  brought  back  to  Cali- 
fornia, where  they  succeeded  in  saving  this  very  important 
industry. 

In  gathering  cocoons  of  moths,  it  will  be  frequently  found 
that  the  interior  is  filled  with  a  large  number  of  small  larvae  or 
their  cast-off  skins.  The  reason  for  this  is  that  an  insect 
called  an  ichneumon  fly,  a  relative  of  the  wasps,  punctured 
the  skin  of  the  moth  larva  and  deposited  a  number  of  eggs. 
These  eggs  developed  into  small  larvae  which  finally  com- 
pletely devoured  the  body  of  their  host.  From  these  larvae 
adult  ichneumon  flies  develop  which  in  turn  are  ready  to 
attack  other  caterpillars  which  are  injurious  to  vegetation. 
It  is  thought  that  parasitic  insects  like  the  ichneumon  flies 


INSECT  ENEMIES  OF  PLANTS 


377 


do  more  to  keep  in  check  the  increase  of  injurious  insects 
than  all  our  artificial  methods. 

Epidemics  among  insects  caused  by  molds  or  bacteria 
sometimes  also  destroy  enormous  numbers  of  them. 

It  very  frequently  happens  that  the  year  in  which  some 


FIGURE  295.  —  LADYBIRD  BEETLE  FEEDING  ON  SCALE  INSECTS. 
Note  that  both  larvae  and  adults  feed  on  scale  insects. 

insect  has  been  a  pest  is  followed  by  one  in  which  there  are 
very  few  of  that  kind  of  insect.  Can  you  suggest  a  reason 
for  this? 

Many  species  of  birds  live  entirely  on  insects  and  others 


378  GENERAL   SCIENCE 

during  a  portion  of  the  year  subsist  chiefly  on  insects.  Many 
birds  that  are  not  primarily  insect  feeders  supply  a  diet  of 
insects  for  their  young.  Students  of  the  subject  estimate 


FIGURE  296. — TOADS  EATING  CATERPILLARS. 

that  birds,  by  destroying  harmful  insects,  each  year  save 
crops  worth  many  millions  of  dollars. 

Toads,  snakes,  and  bats  are  other  animals  that  deserve 
protection  from  man  because  of  their  value  in  destroying 
injurious  insects. 

SUGGESTED  INDIVIDUAL  PROJECTS 

1.  Make  a  collection  showing  the  various  ways  in  which  insects 
injure  plants. 

2.  Make  a  collection  of  injurious  insects  and  give  a  brief  account  of 
the  harm  done  by  each  kind. 

3.  Protect  the  fruit  of  an  apple  tree  from  injury  by  the  codling  moth. 

4.  Make  life  history  cases  of  a  number  of  injurious  insects. 

REPORTS 

1.  The  work  of  the  U.  S.  Bureau  of  Agriculture  in  helping  the  farmer 
in  his  fight  against  insects. 

2.  An  account  of  the  introduction  of  the  gypsy  moth,  of  the  harm 
done  by  it,  and  of  the  efforts  made  to  check  it. 

3.  An  account  of  the  life  history ;  of  harm  done  by  them ;  methods 
used  to  tight  them :  potato  beetle,  cotton  boll  weevil,  codling  moth, 


INSECT  ENEMIES  OF  PLANTS  379 

Hessian  fly,  San  Jose  scale,  chinch  bug,  grasshopper,  brown-tailed  moth, 
army  worm,  etc. 

4.   Work  of  birds  in  destroying  harmful  insects. 

REFERENCES  FOR  PROJECT  XXXI 

1.  Insects  Injurious  to  the  Household  and  Annoying  to  Man,  G.  W. 
Herrick.     Macmillan  Company. 

2.  Insect  Pests  of  Farm,  Garden,  and  Orchard,  E.  D.  Sanderson. 
John  Wiley  &  Co. 

3.  Farmers'  Bulletins. 

4.  Farm  Friends  and  Farm  Foes,  C.  M.  Weed.     Ginn  &  Co. 

5.  Birds  of  Village  and  Field,  F.  I.  Merriam.     Houghton  Mifflin 
Company. 

6.  Book  of  Birds,  Vols.  I  and  II,  Miller.    Houghton  Mifflin  Company. 

GENERAL  REFERENCE  BOOKS 

Child's  Book  of  Knowledge,  Grolier  Co.,  New  York. 

The  Book  of  Wonders,  Presbrey  Syndicate,  New  York. 

Wonders  of  Science,  E.  M.  Tappan,  editor.  Houghton  Mifflin 
Company. 

The  Story-Book  of  Science,  Fabre.     Century  Company. 

Modern  Triumphs,  E.  M.  Tappan,  editor.  Houghton  Mifflin 
Company. 

Wonders  of  Physical  Science,  E.  E.  Fournier.     Macmillan  Company. 

Field  and  Forest  Handbook,  D.  C.  Beard.     Scribners. 

Romance  of  Modern  Inventions,  A.  Williams.  J.  B.  Lippincott 
Company. 

Stories  of  Useful  Inventions,  S.  C.  Forman.     Century  Company. 

Stories  of  Great  Inventions,  E.  E.  Burns.     Harper  &  Bros. 

Makers  of  Many  Things,  E.  M.  Tappan.    Houghton  Mifflin  Company, 

The  Boys'  Own  Book  of  Great  Inventions,  F.  L.  Darrow.  Mac- 
millan Company. 

Handicraft  for  Handy  Boys,  Hall.     Lothrop,  Lee  &  Co: 

The  Boy  Craftsman,  Hall.     Lothrop,  Lee  &  Co. 

Scientific  American  Boy  at  School,  Bond.     Munn  &  Co. 

Harper's  Outdoor  Book  for  Boys.     Harper  &  Bros. 


380  GENERAL  SCIENCE 

Everyday  Physics,  Packard.     Ginn  &  Co. 

The  Wonders  of  Modern  Mechanism,  C.  H.  Cochrane.  J.  £.  Lippin- 
cott  Company. 

The  Land  We  Live  In,  O.  W.  Price.     Small,  Maynard  &  Co. 

Uncle  Sam's  Business,  C.  Mariott.     Harper  &  Bros. 

Commercial  and  Industrial  Geography,  Heller  and  Bishop.  Ginn 
&Co. 

With  Men  Who  Do  Things,  Bond.     Munn  &  Co. 

Pioneers  of  Science  in  America,  W.  J.  Youmans.     D.  Appleton  &  Co. 

Famous  Men  of  Science,  S.  K.  Bolton.  T.  Y.  Crowell  &  Co.,  New 
York. 

How  It  Works,  A.  Williams.     Thos.  Nelson  &  Sons. 

Romance  of  Modern  Engineering,  A.  Williams.  Seeley  Service 
Company.  London. 

Great  American  Industries,  W.  F.  Rocheleau.  A.  Flanagan  Company, 
Chicago. 

A  Source  Book  of  Biological  Nature  Study,  Downing.  University  of 
Chicago  Press. 

Chemistry  of  the  Home,  Weed.     American  Book  Company. 

Chemistry  of  Common  Things,  Brownlee,  etc.     Allyn  and  Bacon. 

Boys'  Book  of  Chemistry,  Clark.     E.  P.  Dutton  &  Co. 

Farm  Science,  W.  J.  Spellman.     World  Book  Company. 

Commercial  Raw  Materials,  Chas.  R.  Toothaker.     Ginn  &  Co. 

Scientific  American  Reference  Book,  Hopkins  and  Bond.  Munn 
&Co. 

Measurements  for  the  Household.  Bureau  of  Standards,  Washing- 
ton, D.  C. 

World  Almanac.     New  York  World. 

Official  Handbook,  Boy  Scouts  of  America.     Doubleday,  Page  &  Co. 

Occupations,  E.  B.  Gowin  and  A.  W.  Wheatley.     Ginn  &  Co. 

The  Story  of  Iron  and  Steel,  J.  R.  Smith.     D.  Appleton  &  Co. 

The  Story  of  the  Submarine,  Bishop.     Century  Company. 

Practical  Physics,  Carhart  and  Chute.     Allyn  and  Bacon. 


APPENDIX 

I.    AVERAGE  RISE  AND  FALL  OF  TIDE 


PLACES 

Feet 

Inch. 

PLACES 

Feet 

Inch. 

Baltimore,  Md.    ... 
Boston  Mass 

1 

9 

*  2 

7 

Old  Point  Comf  t,  Va. 
Balboa  Panama 

2 
12 

6 

Q 

Charleston,  S.  C.  .  .  . 
Colon,  Panama    .  .  . 
Eastport,  Me  
Galveston,  Tex.   .  .  . 
Key  West,  Fla.    .  .  . 
Mobile,  Ala  

5 
0 

18 
1 
1 
1 

2 
11 
2 

0 

2 
6 

Philadelphia,  Pa.    .  . 
Portland,  Me  
San  Diego,  Cal.    .  .  . 
Sandy  Hook,  N.  J.  .  . 
San  Francisco,  Cal.  . 
Savannah,  Ga  

5 
8 
3 
4 
3 
6 

4 
11 
11 
8 
11 
6 

New  London,  Ct.    .  . 
New  Orleans,  La.    .  . 

2 
None 

6 
None 

Seattle,  Wash  
Tampa  Fla  

11 

2 

4 

2 

Newport  R  I    .  . 

3 

6 

Washington  D  C 

2 

11 

New  York,  N.Y.    .  . 

4 

5 

II. 


Highest  tide  at  Eastport,  Maine,  218  inches.     Lowest  tide  in 
United  States  at  Galveston,  Texas,  12  inches. 

SPECIFIC  GRAVITY  OF  SOME  COMMON  SUBSTANCES 
LIQUIDS 


Water 100 

Sea  Water 103 

Dead  Sea    .  .    .     124 


Alcohol 84 

Turpentine 99 

Milk.  .  103 


SOLIDS 


Cork 24 

Poplar  Wood 38 

Maple  Wood 75 

Ice 92 

Butter 94 

Coal 130 

Marble 270 

Glass 289 

The  weight  of  a  cubic  foot  of  distilled  water  at  a  temperature  of 
60°  F.  is  1000  ounces  avoirdupois,  therefore  the  weight  (in  ounces, 
avoirdupois)  of  a  cubic  foot  of  any  of  the  substances  in  the  table  above 
is  found  by  multiplying  the  specific  gravities  by  10. 

381 


Granite 278 

Steel 783 

Copper 895 

Silver 1.047 

Lead 1.135 

Gold 1.926 

Platinum    .  2.150 


382  GENERAL  SCIENCE 

III.    COMPARATIVE  SCALES  OF  THERMOMETERS 


Centi- 

j 

Fahren- 

Centi- 

Fahren- 

grade, 
100° 

heit,  212° 

WATER  BOILS 
AT   SEA- 

grade, 
100° 

heit,  212° 

95 

203 

LEVEL 

20 

68 

90 

194 

15.3 

60 

Temperate 

85 

185 

12.8 

55 

78.9 

174 

10 

50 

75 

167 

Alcohol  Boils 

7.2 

45 

70 

158 

5 

41 

65 

149 

1.7 

35 

60 

140 

0 

32 

WATER 

55 

131 

—1.1 

30 

FREEZES 

52.8 

127 

Tallow  Melts 

—5 

23 

50 

122 

—6.7 

20 

45 

113 

—10 

14 

42.2 

108 

—12.2 

10 

40 

104 

—15 

5 

36.7 

98 

Blood  Heat 

—17.8 

0 

ZERO  FAHR. 

35 

95 

—20 

—4 

32.2 

90 

—25 

—13 

30 

86 

—30 

—22 

26.7 

80 

—35 

—31 

25 

77 

—40 

—40 

IV.    COMPARISON  OF  SOME  COMMON  UNITS  OF 
MEASUREMENT 

1  inch  equals  2.54       centimeters 

1  centimeter  "          .3937    inches 

1  foot  "          .3048    meters . 

1  meter  "  3.28083  feet 

1  yard  "          .9144   meters 

1  meter  "  1.0936    yards 

1  mile  "  1.60935  kilometers 

1  kilometer  "          .62137  miles 


APPENDIX 

liter               equals   1.0567    quarts  liquid 
quart  (liq.)       "           .9463    liters 
quart  (dry)       "         1.1012    liters 
liter                   "          .9081    quarts  dry 
gallon                "        3.78543  liters 
1  liter                   "          .26417  gallons 

1  ounce  (av.)       " 
1  gram 
1  pound               " 
1  kilo 

28.35       grams 
.035      ounces  (av.) 
.45359  kilos 
2.2046    pounds 

1  gallon  of  water 
1  gallon 
1  cubic  foot 
1  gallon 
1  cubic  foot  of  water  (4°  C.) 

weighs      8.345     pounds  , 
equals        .13368  cubic  feet 
"           7.48052  gallons 
"       231.           cubic  inches 
weighs    62.425     pounds 

383 


1  ton  anthracite  coal  occupies  40-43  cubic  feet 
1  ton  bituminous  coal      "        40-48  cubic  feet 


V.  PREPARATION  OF  AGAR  CULTURE  MEDIUM 

Place  500  grams,  about  one  pound,  of  finely  chopped  lean  beef  in 
1000  cc.  of  distilled  water  and  keep  in  an  ice  box  overnight.  Strain 
and  squeeze  out  the  juice.  Boil  the  juice  for  half  an  hour  to  coagulate 
the  albumins.  Filter  and  add  sufficient  distilled  water  to  bring  the 
amount  up  to  1000  cc. 

The  use  of  3  grams  of  a  standard  meat  extract,  such  as  Liebig's,  to 
1000  cc.  of  water  may  be  used  instead  of  the  fresh  meat. 

Ten  grams  of  peptone  should  be  carefully  stirred  in  and  dissolved  by 
boiling. 

Add  sufficient  sodium  hydroxide  to  make  the  reaction  of  the  broth 
neutral  or  slightly  alkaline  to  litmus. 

Chop  into  fine  pieces  15  grams  of  pure  thread  agar.  Dissolve  the 
chopped  agar  in  a  small  quantity  of  boiling  water.  Add  this  to  the 
hot  broth.  Filter  the  broth  containing  the  agar  through  a  filter  made 
of  cheese-cloth,  enclosing  a  layer  of  absorbent  cotton.  Filtration  will 
be  facilitated  by  first  wetting  the  filter  and  funnel  with  boiling  water. 
Sterilize  in  an  autoclave  and  pour  into  sterilized  Petri  dishes. 


384  GENERAL   SCIENCE 


VI.    CLASSIFICATION  OF  ROCKS  AND  DIVISIONS  OF 
GEOLOGIC  TIME 

(Prepared  by  the  U.  S.  Geological  Survey) 

•  The  rocks  composing  the  earth's  crust  are  grouped  by  geologists  into 
three  great  classes,  igneous,  sedimentary,  and  metamorphic.  The 
igneous  rocks  have  solidified  from  a  molten  state.  Those  that  have 
solidified  beneath  the  surface  are  known  as  intrusive  rocks.  Those  that 
have  flowed  out  over  the  surface  are  known  as  effusive  rocks,  extrusive 
rocks,  or  lavas.  The  term  volcanic  rock  includes  not  only  lavas  but 
bombs,  pumice,  tuff,  volcanic  ash  and  other  fragmental  materials  thrown 
out  from  volcanoes.  Sedimentary  rocks  are  formed  by  the  accumula- 
tion of  sediment  in  water  (aqueous  deposits  or  eolian  deposits).  The 
sediment  may  consist  of  rock  fragments  or  particles  of  various  sizes 
(conglomerate  sandstone,  shale) ;  of  the  remains  or  products  of  animals 
or  plants  (certain  limestones  and  coal) ;  of  the  product  -of  chemical 
action  or  of  evaporation  (salt,  gypsum,  etc.) ;  or  of  mixtures  of  these 
materials.  A  characteristic  feature  of  sedimentary  deposits  is  a  layered 
structure  known  as  bedding  or  stratification.  Metamorphic  rocks  are 
derivatives  of  igneous  or  sedimentary  rocks  produced  through  mechani- 
cal or  chemical  activities  in  the  earth's  crust.  The  unaltered  sedi- 
mentary rocks  are  commonly  stratified,  and  it  is  from  their  order  of 
succession  and  that  of  their  contained  fossils  that  the  fundamental 
data  of  historical  geology  have  been  deduced. 


APPENDIX 


385 


ERA 

PERIOD 

EPOCH 

CHARACTERISTIC  LIFE 

Cenozoic 
(Recent  Life) 

Quaternary 

Recent  Pleisto- 
cene (Great 
Ice  Age  ) 

"  Age  of  man."  Animals 
and  plants  of  modern 
types. 

Tertiary 

Pliocene 
Miocene 
Oligocene 
Eocene 

"  Age  of  mammals."  Pos- 
sible first  appearance  of 
man.  .  Rise  and  develop- 
ment of  highest  orders 
of  plants. 

Mesozoic 
(Intermediate 
Life) 

Cretaceous 

Upper 
Lower 

"Age  of  reptiles."  Rise 
and  culmination  of  huge 
land  reptiles  (dinosaurs)  . 
First  appearance  of  birds 
and  mammals  ;  palms 
and  hardwood  trees. 

Jurassic 

Triassic 

Paleozoic 
(Old  Life) 

Carbonifer- 
ous 

Permian 
Pennsylvanian 
Mississippian 

"Age  of  amphibians." 
Dominance  of  tree  ferns 
and  huge  mosses.  Primi- 
tive flowering  plants  and 
earliest  cone-bearing 
trees.  Beginnings  of 
backboned  land  animals  . 
Insects. 

Devonian 

"Age  of  fishes."  Shell- 
fish (mollusks)  also 
abundant.  Rise  of  am- 
phibians and  land  plants  . 

Silurian 

Shell-forming  sea  animals 
dominant.  Rise  of  fishes 
and  of  reef  -  building 
corals. 

Ordovician 

Shell-formingseaanimals. 
Culmination  of  the  bug- 
like  marine  crustaceans 
known  as  trilobites. 
First  trace  of  insect  life. 

Cambrian 

Trilobites,  brachiopods 
and  other  sea  shells. 
Seaweeds  (algse)  abun- 
dant. No  trace  of  land 
animals. 

Proterozoic 
(Primordial 
Life) 

Algonkian 

First  life  that  has  left  dis- 
tinct record.  Crusta- 
ceans, brachiopods  and 
seaweeds. 

Archean 

Crystalline 
Rocks 

No  fossils  found. 

386 


GENERAL   SCIENCE 


The  first  striking  fact  in  the  geological  history  of  climate  is  that  the 
present  climate  of  the  world  has  been  maintained  since  the  date  of  the 
earliest,  unaltered,  sedimentary  deposits.  The  oldest  sandstones  of  the 
Scotch  Highlands  and  the  English  Longmynds  show  that  in  pre-Cam- 
brian  times  the  winds  had  the  same  strength,  the  raindrops  were  of  the 
same  size,  and  they  fell  with  the  same  force  as  at  the  present  day. 
The  evidence  of  paleontology  proves  that  the  climatic  zones  of  the  earth 
have  been  concentric  with  the  poles  as  far  back  as  its  records  go ;  the 
salts  deposited  by  the  evaporation  of  early  Paleozoic  lagoons  show  that 
the  oldest  seas  contained  the  same  materials  in  solution  as  the  modern 
oceans;  and  glaciations  have  recurred  in  Arctic  and,  under  special 
geographical  conditions,  also  in  temperate  regions  at  various  periods 
throughout  geological  time.  The  mean  climate  of  the  world  has  been 
fairly  constant,  though  there  have  been  local  variations  which  have  led 
to  the  development  of  glaciers  in  regions  now  ice  free,  at  various  points 
'in  the  geological  scale.  That  there  has  been  no  progressive  chilling  of 
the  earth  since  the  date  of  the  oldest  known  sedimentary  rocks  is  shown 
by  their  lithological  characters  and  by  the  recurrence  of  glacial  deposits, 
some  of  which  were  laid  down  at  low  levels  at  intervals  throughout 
geological  time. 

VII.    SOLAR  SYSTEM 


GRAVITY 

AT  SUR- 

TIME OF  REVO- 

DISTANCE FROM  SUN 

RADIUS 

FACE. 

LUTION  AROUND 

EARTH 

SUN 

=  1 

Mercury 

35,960,500  miles 

1504  miles 

.38 

88  days 

Venus 

67,195,600     " 

3787     " 

.89 

225     " 

Earth 

92,897,400     " 

3958     " 

1.00 

365^     " 

Mars 

141,546,600     " 

2107     " 

.38 

687     " 

Jupiter 

483,327,000     " 

43,341     " 

2.66 

4332     i'~ 

Saturn 

886,134,000     " 

36,166     " 

1.14 

10,759     *' 

Uranus 

1,782,792,000     " 

15,439     " 

.96 

30,688     " 

Neptune 

2,793,487,000     " 

16,465     " 

.98 

60,178     " 

Sun 

432,196     " 

27.98 

Moon  : — Diameter,  2160  miles;  average  distance  from  Earth,  238,862 
miles;  time  of  revolution  around  the  Earth,  27.32  days;  force  of 
gravity  at  surface  of  Moon,  one-sixth  of  the  force  of  gravity  at 
surface  of  Earth. 


APPENDIX  387 


VIII.    BIRD  COUNT  IN  THE  UNITED  STATES 

(By  E.  W.  Nelson,  Chief  of  the  Bureau  of  Biological  Survey,  United 
States  Department  of  Agriculture) 

Early  in  the  summer  of  1914  the  Biological  Survey  of  the  United 
States  Department  of  Agriculture  took  initial  steps  toward  a  count  of 
the  birds  of  the  United  States  for  the  purpose  of  ascertaining  approxi- 
mately the  number  and  relative  abundance  of  the  different  species. 
This  preliminary  count  proved  to  be  so  satisfactory  that  the  Survey 
repeated  it  on  a  larger  scale  in  1915,  and  extended  it  over  a  still  greater 
area  in  1916  and  1917.  The  results  obtained  in  1914  have  been  sur- 
prisingly corroborated  by  those  of  succeeding  year  ,  and  the  work  gives 
promise  of  producing,  after  a  series  of  years,  results  that,  in  view  of  the 
recognized  value  of  birds  to  agriculture,  cannot  fail  to  be  of  great  value. 
It  has  been  ascertained  through  these  counts  that  birds  in  the  agricul- 
tural- districts  in  the  Northeastern  United  States  average  slightly  more 
than  a  pair  to  the  acre,  though  in  parts  of  the  arid  West  and  oh  the 
treeless  plains  this  number  dwindles  to  an  average  of  half  a  pair,  or 
even  less,  to  the  acre. 

By  far  the  most  abundant  birds  in  the  United  States  are  the  robin 
and  the  English  sparrow,  but  several  others  are  common  enough  to 
make  their  total  numbers  run  well  into  the  millions.  The  counts  so  far 
show  that  the  most  abundant  bird  on  farms  in  the  Northeastern  States 
is  the  robin ;  next  to  this  is  the  English  sparrow,  and  following  these 
are  the  catbird,  brown  thrasher,  house  wren,  kingbird,  and  bluebird, 
in  the  order  named.  The  densest  bird  population  anywhere  recorded 
is  near  Washington,  D.  C.,  where  a  careful  count  showed,  in  1915,  one 
hundred  and  thirty -five  pairs  of  forty  species  on  five  acres.  Two  city 
blocks,  well  furnished  with  trees,  in  the  city  of  Aiken,  S.  C.,  harbored 
sixty-five  pairs  on  ten  acres.  These  high  figures  show  the  important 
results  which  will  follow  from  careful  protection  and  encouragement  of 
birds. 


INDEX 

References  are  to  pages 


Accommodation  of  eye     .    .   290-291 

Acetic  acid 126 

Adir  ndack  Mountains,  relation 

to  Hudson  River    .    .    .    178-182 

Aeration  of  water 165-166 

Agar 94 

Agriculture,  affected  by  irrigation  136 
Agrimonte,  Dr.,  member  of  Yel- 
low Fever  Commission   .    .187 

Air,  composition 80 

compressed 17-24 

conductor  of  sound 49 

effect  of  heating 28 

force  in  motion 2 

heating  by  hot  air     ...   304-305 
inspired  and  expired     .    .    .   65-66 

pressure 5,  6,  7,9 

relation  of  moisture  to  com- 
fort          142-143 

weight 4,  5 

Airplane 1-4 

Alcohol,  changed  into  acetic  acid 

by  bacteria 125 

Aldebaran,  a  fixed  star      ....   209 

Alimentary  canal       346 

Ammeter 260 

Amoeba,  causfe  of  disease  of  teeth   111 

Ampere       260 

Antenna,  of  wireless  telegraphy  .   262 

Anthers 353 

Antiseptics 108,120 

use  of 119-121 

Antitoxin,   preparation  of    diph- 
theria      117-118 

importance  of  early  use     .    118-119 
Appetite,  as  a  guide  in  eating     .   337 

Apple  worm 370-371,  373 

Aquarium,  balanced      ....   89-91 

Arc  light 270-271 

Armature,  of  dynamo 264 

of  electric  bell 254 

of  motor  .   265 


Arms,  of  a  lever 231 

Arsenate  of  lead,  as  an  insecti- 
cide      373 

Artesian  wells 166 

Astigmatism 292-293 

Audion  detectors,  wireless       .    .   262 

Auriga,  a  constellation     ....   207 

Automobile,  engine  ....   246-249 

gears  for  high  and  low  speed  .   234 

source  of  power 57-58 

Automobile  tires   ....     13, 19,  20 
Autumnal  equinox 212 

Bacteria      61,  93 

action  of,  on  sewage 172 

cause  of  decay  of  food.    .    .   92-93 
conditions        favorable        for 

growth 96-97 

destruction  of,  in  rivers   .    .    .173 
in  water  supply  reservoirs   .    1 65 
growth      affected      by    disin- 
fectants and  antiseptics    1 1 9- 1 20 
importance    in     causing     de- 
cay      125-126 

important  in  production  of 
leather,  curing  tobacco, 
preparing  linen,  and  in  mak- 
ing vinegar  125-126 

necessary  in  soil 318 

nitrogen-fixing 123-124 

producing  flavor  of  butter   .    .    125 

of  cheese 125 

where  found 93-94 

Balanced  aquarium 89-90 

Ball  bearings,  use  in  preventing 

friction 243 

Balloon 10 

Barometer,  aneroid 8-9 

mercury 6-7 

Bats',  value  in  destroying  insects .   378 

Battery,  storage 271-273 

Bee,  adaptation  for  pollination  .  359 


INDEX 


References  are  to  pages 


Beetle,  lady  bird       ....  375-376 

Bell,  electric 253-254 

Belts,  use  in  machinery   ....   235 

Bends 19 

Benzoate  of  soda,  use  as  an  anti- 
septic . 120 

Betelgeuse,  a  fixed  star  ....  209 
Bicycle,  application  of  power  to 

drive  wheel 235 

Big  Dipper 205 

Bile .346 

Binding  posts,  of  electrical  ap- 
paratus    254 

Birds,  value  in  destroying  insects   378 

Block  and  tackle 237 

Blood  corpuscles,  white    .    .   109,114 

Blood  poisoning 110 

Blood  system 347 

Blueprints 222-223 

Blue  vitriol 258 

Blueness  of  sky 288 

Boils 110 

Bone  meal,  use  as  a  fertilizer  .  326 
Bones  of  body  as  levers  ....  233 

Boyle's  law 18 

Brain,    interpretations    of    light 

impressions 295 

Brakes,  use  in  overcoming  inertia  244 
Bread,  composition  of  ....  332 
Breathing,  of  animals  ....  69-72 

of  human  body 67 

of  plants 67-69 

reason  for  breathing  through 

nose 114. 

Breathing  movements      ....     12 

Bull,  a  constellation 209 

Bunsen  burner 56 

Buoyancy 10-11 

Burbank,  Luther,      367 

Burning  ; 54-56 

destruction 74-79 

Butter,     flavor      improved      by 

growth  of  bacteria    .    .    .    .125 
Butterfly,  adaptation  for  pol- 
lination     358-359 

Caisson       18 

Calorie 335 

Calorimeter 334 

Calyx 352 


Camera,  similarity  to  eye     .    .    .  289 

focusing 291 

Canal,  alimentary 346 

Canals,  importance  in  navi- 
gation          183-186 

Candle  power,  measurement  of   .   281 

Capella,  a  fixed  star 207 

Capillaries      72 

Carbohydrates,    importance     as 

food 331 

manufacture  of 82-85 

Carbon  dioxide      .......     55 

action  on  rocks 312 

amount  removed  from  air  by 

plants 85-87 

percentage  in  air 80 

proof      of      use      in      starch- 
making   84-85 

Carboniferous  period 88 

Carburetor 246 

Carrol,  Dr.,  member  of   Yellow 

Fever  Commission   .    .    .    .187 
Cassiopeia's    Chair,    a    constel- 
lation      :    .    .    .   207 

Catskill  Mountains,  as  a  source  of 

water  supply 161 

Caves,    formation   in   limestone 

regions 168 

produced  by  action  of  carbon 

dioxide  in  water 312 

Cell,  dry .259 

gravity 258 

storage    271-272 

Cells,  plant 148 

Cell-sap 147 

Centrifugal  force,  examples 

of 197-198 

Cepheus,  a  constellation      .   206,  207 
Chain  drive,  bicycles  and  motor 

trucks 235 

Charioteer,  a  constellation  .    .    .   207 
Cheese,  flavor  produced  by  bac- 
teria and  molds 125 

Chemical  change,  oxidation     .    .     55 
in  electric  cells   .......   258 

in  making  picture,  caused 

by  energy  of  sun.    .    .   221-223 
of  storage  cell        ....   271-272 

Chemical  elements 56 

in  soil      324 

necessary  for  growth  of  plants  324 


INDEX 


References  are  to  pages 


Chicago  drainage  canal  .  .  .  .173 
Chisel,  as  an  inclined  plane  .  .  240 
Chlorine  gas,  use  in  sterilizing 

water 166 

Chlorophyll,    necessary        for 

starch-making 88-89 

Chronometer,  use  in  determining 

longitude 217 

Ciliary  muscle 292 

Circulation  of  blood,  need  for      .     67 

Circulatory  system 347 

Clay,  as  a  constituent  of  soil  309-310 
Clothing,  for  winter  and  summer  301 

light  effects  of 297 

Clouds 

formation  of  ......    131—132 

Clover,  effect  upon  soil  of   ...    123 
Coal,   bituminous    and    anthra- 
cite     85-86 

burning  of 63-64 

origin 85-86 

Coal  famine,  results  of     ....     63 

Coffee  grinder 234 

Cogwheels 234-235 

Coils,  electric,  of  electric  bell   .    .   254 
Cold,  extremes  of  heat  and  cold  in 
lessening  resistance  to  dis- 
ease      114 

Cold  frame 223-224 

Colds,  caused  by  bacteria    ...    110 
Cold-storage  cars  and  ships,  im- 
portance of 103 

Cold-storage  plants  ....   100-103 

Color,  explanation  of    ...   286-287 

importance  of  color  of  flowers    358 

of  clothing 297 

of  sunset  and  sunrise    ....   288 
relation       of       wall-color     to 

lighting 285-286 

Communicable  diseases  ....  Ill 
Commutator,  effect  on  alternating 

current 264 

Compounds,  chemical 56 

Concave  lens,  for  correction  of 

near-sightedness 292 

Constellations 205 

Constipation       346-347 

Consumption    (tuberculosis), 

transmission  of 112 

Convection  currents,  of  air  .  28-29 
,  of  water 306-307 


Convex  lens,  for  correction  of 

far-sightedness 292 

Cooking  appliances,  electric    .    .  268 

Copper-plating       266 

Corn,  primitive      . 362 

Cornea  of  eye 289 

Corolla .    .  353 

Cotton  seed  meal,    use    as    fer- 
tilizer    324 

Cowpox       116 

Crankshaft 247 

Cross-pollination 355 

Crow  bar 231 

Crystal  detectors,  wireless       .    .  262 

Culture  media 93 

Cyclones     . 36 

Dams,    use    in    developing 

water  power       ....   153-157 

Daniell  cell 258-259 

Darwin,  Charles 355 

Day-light  saving 216 

Decay,  cause  of 92-93 

importance  of 122-123 

Detectors,  wireless 262 

Developer,  in  photography     .    .   221 
Dew,  formation  of    ....    127-128 

Dew  point 128 

Diet,  amount  of  food  in  .    .   336-342 
good,    as    protection    against 

disease 114 

importance     of     green    vege- 
tables and  milk  in     .    .   332-333 
of  mineral  matter  in.    .   331-332 

of  lumbermen 330 

planning  of 342-343 

value  of  fat  in 330-331 

value  of  starch  and  sugar  in .    .   331 
use  of  orange  juice  in   .    .    .    .104 

Digestion 343-344 

in  human  body      ......   346 

of  starch 345 

Diphtheria,  transmission  of.    .    .    113 
Direct  lighting  .....;..   284 

Dirigible 10 

Diseases,  carried  by  milk    .    .    .    103 

communicable .111 

natural  protection  against       .    114 

of  eyes .   294 

Disinfectants 108, 120 

use  of 119-121 


INDEX 


References  are  to  pages 


Domestication    of     plants     and 

animals 362-363 

Draft,  of  furnace 307 

Dragon,  a  constellation    ....   207 
Dragon  fly      .........   375 

Dry  cell  .    . 259 

Drying,    as   a    means    of    food 

preservation       ....    105-106 

Dust,  carrier  of  bacteria  ....      94 

effect  upon  sunset  colors    .    .   288 

Dynamo 262-264 

Ear,  human 50-52 

Earthworm,  breathing  of      ...      69 

Eclipses 202-203 

Edison,  Thomas  A 270 

Efficiency  of  machines     ....   241 

of  engines       245-246 

of  storage  cell 272 

Egg  cell 354-355 

Electric  cells 257-259 

in  series 260 

Electric  current,  alternating  and 

direct 264 

generated  by  cells     .    .    .   257-259 
by  dynamo 262-264 

in     electroplating     and    elec- 
trotyping 266-267 

used  to  produce  heat    .    .   267-268 

use  in  refining  metals    ....   267 

Electric  furnace 268 

Electric    heating    and    cooking 

appliances 268 

Electric  lights '.   268-271 

Electric  transformer 270 

Electrical  pressure    ...:..  259 
Electricity,  early  use  of     ....   252 

relation  of  water  power  to  153-157 

static      .    .    .    .    : 273 

Electro-magnet 255-256 

use  in  dynamo       264 

Electromotive  force 259 

Electroplating 266 

Electrotyping "...   267 

Elements,  chemical 56 

Embryo 350 

Energy 63 

available  in  human  body     .    .     67 

Engines,  gas 246-249 

four-stroke  cycle 247 

solar    .  .   224-225 


Engines  —  Continuued 

inefficiency  of 225 

Enzyme 345 

Equilibrium,  stable  and  unstable    194 
Equinox,  vernal,  autumnal      .    .   212 

Erosion,  stream 179 

wind 314 

Eustachian  tube 51-52 

Evaporation   .    .    . . 26, 77 

in  cold-storage  plants       .    100-101 
in  iceless  refrigerator    .    .      99-100 
Expansion  tank,  hot  water  heat- 
ing system      .    .   ' 305 

Eye,  abuse  of     ......   293-294 

advantage  of  two  eyes ....   293 

care  of 293-294 

normal 289 

Eye  strain 293 

Eyeglasses,  use  of     ....   291-293 

Fading  of  colors 223 

Far-sightedness 288 

cause  and  correction  of    .   291-292 

Fat,  use  in  food 330 

Fatigue,  excessive,  lessening  re- 
sistance to  disease     .    .    .    .114 
Fermentation,  by  yeast   .    .    .    .    104 

in  sauerkraut 105 

Fertilization,  of  egg  cell   .    .   354-355 
Fertilizer,  nitrate  of  soda  as    .    .   324 

organic  matter  as 324 

sewage  used  as  .......    173 

sulphate  of  ammonia  as       .    .   324 
Field  magnet,  of  dynamo    .    .    .   264 

of  motor 265 

Filaments 353 

Filaments,  of  electric  light  bulbs    269 

Film,  photographic 221 

Fire  extinguisher 76 

Fire  lanes 78 

Fire  walls 79 

Fireless  cooker 301 

Fireproof  construction      ....     79 

Fish,  breathing  of 71-72 

in  balanced  aquarium  .    .    .   89-91 

use  as  fertilizer 324 

Fishing  pole,  as  a  lever    ....  233 

Flame 59 

Flies,  relation  to  typhoid 

fever 112, 172 

Floods,  prevented  by  forests    181-182 


INDEX 


References  are  to  pages 


Flower,  purpose  of 352 

structure  of 352-353 

Fly  wheel,  advantage  of  .    .    .    .-  247 

Focus,  of  camera .   291 

of  eye 290-291 

Fog,  formation  of      ....    131-132 
Food,  composition 

of 332-336,    338-341 

energy  and  tissue  forming  .  89-91 
foods,  rich  in  jiitrogen  .  .  .331 
for  growth  and  repair  .  .  330-331 

preservation       92-106 

rich  in  mineral  matter  .  .  .331 
storage  in  seeds  ....  350-351 

value  as  fuel 66 

Food  principles 331 

Force 228 

measurement  of     ....   229-230 
Forest  fires,  effect  upon  color  of 

sunset 288 

Forests,  injured  by  insects.    .    .   372 

relation  to  floods 181 

relation  to  navigability  of 

rivers  and  harbors    .    .    178-180 
relation  to  water  supply   .    .    .163 

Fountain  pen 13 

Franklin,  Benjamin 273 

Freezing  of  water  in  breaking 

rock 312-313 

Friction,  cause  of 241 

reduction  of 242-243 

value  of 243-245 

Friction  matches 58-59 

Fuel,  denned 65 

Fuel  value  of  foods,  measure- 
ment of   334-336 

Fulcrum,  of  a  lever       231 

Furnace,  electric 268 

hot  air 304-305 

Fuses,  electric .   270 


Galvanized  iron 75 

Gastric  juice      .........  346 

Gears,  automobile 247 

Germicides 120 

Germs 108 

Gills,  offish 72 

Glacial  lakes      317 

Glacial  scratches 316 

Glacier 316-319 


Gorgas,  Dr.  William  C.,  com- 
bating    yellow     fever 

and    malaria 187-188 

Grafting      . 365-360 

Grasses,     ancestors     of     grain 

plants      262 

Gravel,  as  a  constituent  of 

soil 309-310 

Gravitation,  law  of 193 

Gravity,  center  of 194 

Gravity  cell 258 

Grease,  use  to  prevent  fric- 
tion         242-243 

Great  Bear,  a  constellation  .  .  206 
Great  Dipper,  a  constellation  .  205 
Grindstone,  use  in  sharpening 

tools 314 

Guano,  use  as  fertilizer    ....   324 
Guard  cells,  action  of,  in  con- 
trolling transpiration    ...    149 

Hail,  formation  of 134 

Harbors,  caused  by  sunken 

coast 175-178 

importance  of 175 

Hard  water 168 

Headache,  caused  by  eye  strain  293 
Health  increases  resistance  to 

disease   . 114 

Hearing 50-52 

Heat,  absorption  by  land  and 

water 31-32 

conductors  of 303-304 

effect  on  rocks  . 312 

extremes    of    heat    and    cold 
in    lessening    resistance    to 

disease 114 

from  electric  current     .    .   267-268 

from  oxidation 54 

passage  through  glass  ....   224 

value  in  food  preservation    103-104 

Heating  appliances,  electric    .    .   268 

of  houses 304-307 

Helium 12 

Heredity 363-364 

Horse  power      230 

Hotbed      61-62 

Hot  air,  heating  by  ....  304-305 
Hudson  River,  a  submerged 

river  valley 175-177 


INDEX 


References  are  to  pages 


Humidity,  determination  of   142-143 

relative 142 

Humus 310,318 

importance  in  soil 318 

Hurricanes 38-40 

Hybridizing    ..........   365 

Hydraulic  pressure,  source 

of  power  of 157-158 

uses  of 158-159 

Hydrogen .!...-  .    .     12 

Hydrophobia,  Pasteur  treatment 

for 119 

Hygrometer,    to    determine 

humidity    .-..,,   .    .    .    142-143 
Hypo 221 


Ice,  use  in  refrigerator  .    .    . 
Iceless  refrigerator  .    . 
Ichneumon  fly  .    ...    .   ..' 

Illumination  of  a  room     .    . 
Immunity,  acquired      . 

to  diphtheria 

Improvement  of  plants  and 
animals      .    .    .    .   ;   . 
Inclined  planes,  use  of,  ex- 
amples of 

Indirect  lighting    .    .    .    .  • « 
Induction  coil,  use  and  struc- 
ture  

Inertia,  defined 

relation  to  centrifugal 
force    ........ 

Inflammation 

Insecticides 

Insects,  adaptation  for  polli- 
nation      

breathing  of 

carriers  of  disease      .    .    . 

destruction  of  harmful   . 

injurious  to  plants    .    .    . 

yearly  damage  by     ... 

Intestine 

Iron,  galvanized 

Irrigation 


97-99 
.99-100 
.  .  376 
278-286 
115-119 
117-118 

362-367 

238-240 

.   284 


261-262 
.   235 


197-199 
.  .  108 
373-375 

357-359 
.  70-71 
112-113 
373-378 
269-372 
.  .  372 
346-347 
.  .  75 
.  136 


Jackscrew,  use  in  doing  work     .   24Q 
Jenner,  Edward llg 

Kerosene  emulsion,    as    an    in- 
secticide       375 

Kilowatt 261 

Kilowatt  hour    .  .261 


Kindling  temperature  .....     58 

Kite 1-2 

Knife,  as  an  inclined  plane  .  .  240 
Knots,  importance  of  friction  in  245 

Ladybird  beetle 375-376 

Lakes,  glacial 317 

Latitude      218 

Lazear,    Dr.,    martyr    in    fight 

against  yellow  f^ver  ....    188 

Leaf,  work  of 82-89 

Leaf  mulch 322 

Legumes,  effect  upon  soil  of   .    .  124 
Lens,  use  as  magnifying  glass  289-290 
Lenses,  for  correction  of  defec- 
tive vision 292 

Lever,  use  in  doing  work  .  231-233 
Light,  broken  up  by  prism  .  .  .  287 

intensity 279-280 

reflected  and  diffused  .    .   276-277 

refraction  of       289-290 

result  of  oxidation 55 

Lighting  of  rooms,  cost   .    .   278-282 

direct  and  indirect 284 

from  sunlight 276-278 

Lightning 273 

Limestone  composition  ....  56 
Little  Bear,  a  constellation  .  .  207 
Little  Dipper,  a  constellation  .  .  206 

Longitude       214 

Low  pressure  areas 33-36 

Lumber,  injured  by  insects     .    .   369 

Lungs      72 

Luray  Cave,  formation  of    ...   312 

Machines,  efficiency  of    .    .   241-243 

reasons  for  use 228 

Magneto 249 

Magnetic  needle 256-257 

Magnets,  electro-   and  per- 
manent      255-256 

of  dynamo 263-264 

Malaria,  transmission  of  ...  113 
Mammoth  Cave,  formation  of  .  312 
Manure,  use  as  fertilizer  .  .  .  324 
Mars,  possibility  of  life  upon  203-204 
Match,  lighting  of  ......  58-60 

Meat  chopper 234 

Medicine  dropper 11 

Micro-organisms 94, 108 

Micropyle       354-355 


INDEX 


References  are  to  pages 


Microscope,  principle  of  .    .   294-295 

Milk,  condensed 104 

evaporated 106 

importance  in  die^t 343 

pasteurization  of  ....    103-104 
powdered    . 106 

Mineral  matters,  importance  of, 

in  foods       331 

Mizar,  a  fixed  star 207 

Moisture  of  air,  relation  to 

comfort       142-143 

Moisture,  given  off  by  plants  .      145 
taken  up  by  roots  of  plants  145-146 

Mold,  cause  of  decay  of  food    .    .   93 
conditions     favorable     for 

growth 96-97 

importance  in  ripening  cheese  125 

Monsoon 32 

Moon,  eclipse  of 203 

phases 201-202 

relation  to  tides    ....    192-195 
revolution  around  earth  .    .    .    197 

Mosquitoes,  breathing  of    ...      70 

carriers  of  malaria 113 

carriers  of  yellow  fever    ...    188 

"Mother"  of  vinegar 125 

Motion  pictures 295-297 

Motor,  electric 265-266 

gasoline 246-249 

Mountains,  as  a  source  of  water 

supply 161 

Mucus,  importance  in  keeping 
germs  out  of  throat  and 
lungs 114 

Mulch,    importance    in    holding 

water  in  soil       322 

Near-sightedness 288 

cause  and  correction  of    .   291-292 

Nectar 358 

Negative,  in  photography    .    .    .  221 

Nerve,  optic 278 

endings  in  eye    .    .    .".    :   .    .  278 

New  York  City,  water  supply  of  160 
Newton,  Sir  Isaac,    first  law  of 

motion    .    : 198 

law  of  gravitation 193 

Niagara  Falls,  a  source  of  water 

power      155 

Nitrate  of  soda,  use  as  fertilizer  324 


Nitrogen,  fixation  of 325 

foods  containing  much     .    .    .331 
importance  in  the  air     .    .    .   81-82 
necessity  of,  for  making  pro- 
tein       328 

source  of,  for  plants  .  .  .  324-325 
Nitrogen-fixing  bacteria  .  .  123-124 
Nodules,  on  roots  of  plants  of 

clover  family 124 

North  Star 205-206 

value  in  determining  lati- 
tude    .    . 217-218 

Nucleus 354 

Nutrients 331 

Ocean,  cause  of  saltiness     .    .    .   141 

Oculist 293 

Ohm 260 

Ohm,  Georg 260 

Oil,  origin  of,  in  plants    ....   327 
use  to  prevent  friction  .    .   242-243 

Opera  glasses 295 

Optometrist 293 

Organic    matter,     a    source    of 

nitrogen 324 

a  source  of  potassium  and 

phosphorus 325-326 

importance  of  decay  of  .  122-123 
Orion,  a  constellation  .  .  .  208-209 

Osmosis 148 

Ovules 353 

Oxidation 55 

in  human  body 65-67 

in  plants 67-69 

slow 60-62 

Oxygen 55 

given  off  by  plants 84 

percentage  in  air 80 

test  for 84 

Panama  Canal,    importance    in 

ocean  transportation  ...  186 
Paris  green,  as  an  insecticide  .  373 
Pascal's  principle,  in  relation  to 

hydraulic  pressure  ....  158 
Pasteur  treatment  for  rabies  .  119 
Pasteurization  of  milk  .  .  103-104 
Perseus,  a  constellation  ....  207 

Petals 352 

Petri  dish 94 

Phonograph 47-49 


INDEX 


References  are  to  pages 


Phosphate  rock,  use  as  fertilizer  326 
Phosphorus  .  .  .  .  »  .  .  .  .  59 

in  soil      324 

source  of,  as  fertilizer       .   325-326 

Photography 221-222 

Photosynthesis,  denned  ....     84 

Pimples 110 

Pin,  as  an  inclined  plane     .    .    .   240 

Pistil 353 

Pistillate  flowers       ......  356 

Pitchfork,  as  a  lever 233 

Placenta 350 

Planets .   203-204 

Plants,  breathing  of     ....   67-68 

importance   in    a    balanced 

aquarium 89-91 

Pleiades,  a  constellation      .    .    .  209 

Pneumatic  drill 23 

Pneumatic  tubes       23 

Pneumonia,  transmission  of  .  .  113 
Polarization  of  electric  cell  .  .  .  258 
Pole  Star 205-206 

value  in  determining  lati- 
tude        217-218 

Pollen 353 

Pollen  grain 354 

Pollen  tube 354 

Pollination 355 

insect 357-359 

wind 357 

Potassium 56 

in  fertilizers 325-326 

in  soil      . 324 

sources  of 326 

Potatoes,  primitive  condition  .  363 
Power,  of  automobile  .  .  .  57-58 
Prevailing  westerlies  .  .  .  .  .  36 
Prints,  in  photography  ....  222 

blue 222 

Proeyon,  a  fixed  star 209 

Projection  lantern,  use  of  lens  in  295 
Propagation  of  plants,  by  seeds  .  349 

vegetative 365-367 

Proteins      .......  89-90,328 

in  diet 337 

Protozoa 96 

Psychrometer,  in  determination 

of  relative  humidity     ...    142 

Pulleys,  uses  of 235-237 

Pump,  exhaust  air 21 

force    .  .   22-23 


Pump  —  Continued 

suction 14 

tire 21-22 

Pus 109-110 

Push  button,  of  electric  bell  .  .  253 
Pyorrhea Ill 

Rabies    (hydrophobia),    Pasteur 

treatment  for 119 

Radiation,  of  heat 306 

Radiator,  automobile  .  .  .  249, 306 
injured  by  freezing  .  .  .  312-313 
of  heating  plant  ....  305-306 

Rain 40-41 

formation  of 132-133 

Rainbow 41 

Rainfall,  distribution  of  .  .  134-135 
Record  of  phonograph  .  .  .  48-49 
Reed,  Dr=,  member  of  Yellow 

Fever  Commission   ....    187 

Reflectors,  use 282-285 

Refraction  of  light    ....  289-290 

Refrigerator 97-100 

walls  of 301 

Reservoirs,    importance    in 

water  supply  system    .    165, 167 
Resistance,  natural,  of  body 

against  disease  .    .    .    .    .    .114 

Retina  of  eye „    .  291 

Rickets 104 

Rigel,  a  fixed  star 209 

Riggs' disease  of  teeth  .  .  .  .110 
Rocks,  disintegration  of,  in 

formation  of  soil 311 

phosphate 326 

stratified 178,180 

Roller  bearings,  use  in  preventing 

friction 243 

Roots,  extent  of 145-146 

selective  absorption  by  ...    .327 
special  structures  for  taking  in 

moisture 147 

splitting  rocks   „ 313 

Root  hairs,  importance  in  taking 

in  moisture    .......    148 

selective  absorption  by    ...   327 

structure 148 

Rotation   of   earth,   effect  on 

winds 32-33 

Rusting  of  iron      . 60 

prevention  of 75-76 


INDEX 


References  are  to  pages 


Safety  matches 59 

Safety  valve,  of  steam  boiler  .    .   306 

Saliva      346 

Salt,  use  in  food  preservation     .    105 
Sand,  as  a  constituent  of  soil  309-310 

Sand  blast,  action  of 314 

Sauerkraut 105 

Screw,  an  inclined  plane      .    .    .   240 

Sea  breeze 31 

Seasons,  cause  of      ....   211-212 
Seaweed,  as  a  source  of  potas- 
sium     326 

Seed  leaves 350 

Seedlings,  growth  of    .....   350 

Seeds,  formation  of 354 

structure  of 349-352 

See-saw 232 

Selection,  in  improvement  of 

animals  and  plants   .    .   363-364 
Selective  absorption     .....  327 

Self-pollination 355 

prevention  of 356-357 

Sepals 352 

Septic  tank  for  disposal  of  sew- 
age   172 

Seven  Sisters,  a  constellation     .   209 
Sewage,  disposal  of  ....    172-173 

use  as  fertilizer      173 

Shades,  use 282-285 

Silt,  as  a  constituent  of  soil  .    .    .310 

Siphon 14 

Sirius,  a  fixed  star 209 

Skin,    unbroken,    protection 

against  germs 114 

Sky,  blueness  of 288 

Slag,  use  as  fertilizer 326 

Slaughter  house  waste,  use 

as  fertilizer 324,  326 

Sleep,  lack  of,  in  lessening  re- 
sistance to  disease     .    .    .    .114 
Smallpox,  vaccination  against     .    116 
Snakes,  value  in  destroying  in- 
sects     378 

Snow,  formation  of  ....   132-133 
Soil,  composition  of  ....   309-310 

glacial 314-317 

importance    of    bacteria   in 
returning  organic  matter 

to 122-123 

importance  of  legumes  in 

improving 123-124 


Soil  —  Continued 

produced  by  decay  of  organic 
matter 318 

produced  by  erosion     .    .   313-314 

produced  by  weathering  .   311-313 

water-holding  power  of    .   321-323 

Solar  engines 224 

Solar  system .  203 

Sound 44-47 

Sound  box  of  phonograph   .    .  47-48 

Sperm  cell 354 

Spices,  use  in  food  preservation  .  105 
Spontaneous  combustion  ...  61 
Spraying  to  kill  insects  .  .  373-374 
Sprocket  wheel,  bicycle  ....  235 
Staminate  flowers  ....  356-357 

Standard  time 215 

Starch,  composition  of     .    .    .   56,83 

digestion  of 345 

test  for  starch  in  leaf    .    .    .   82-83 
Starch  making,  proof  of,  in 

leaf 82-83 

raw  materials     .:....   83-84 
Stars,  fixed     .    .    .' 209 

value  in  determining  latitude  .   217 

Static  electricity 273 

Steam  heat 304-305 

Stereoscope 293 

Stigma 353 

Stomates,  action  of,  in  control- 
line;  transpiration      ....    150 

Stratified  rocks 178, 180 

Stripes,  effect  of,  in  clothing  .  .  297 
Suez  canal,  importance  in  ocean 

transportation 186 

Sugar,  use  in  food  preservation   .    104 
Sulphate  of  ammonia,  use  as  fer- 
tilizer   324 

Sun,  eclipse 202 

maintenance  of  energy  of   225-226 

source  of  energy  of  coal  and 

wood 86 

source  of  energy  of  gasoline    .   219 

source  of  energy  of  water 

power      153-155 

source  of  energy  of  winds    .    .   220 

use  of  sunlight  in  making 

pictures 221-223 

Sunlight,     use    in    making 

pictures 221-223 

Sun  parlor      223 


10   • 


INDEX 


Sunrise  and  sunset,  color  of  .  .  288 
Sun  time .  214-215 

Taurus,  a  constellation  ....  209 
Teeth,  dangers  from  decay 

of 110-111 

Telegraphy,  wireless     .    .    .   261-262 

Telephone      50 

Telescope,  use  of  lens  in  ...  295 
Temperature,  in  cold  storage 

plant 100 

relation  to  formation  of  dew     128 
Terminal  moraine,  of 

glacier  .  .  .  ' .  .  316-317, 319 
Tetanus,  transmission  of  ...  113 
Thermometer,  wet  and  dry  bulb  142 

Thermos  bottle 300-301 

Thunderstorm 40,41 

Tides,  cause 192 

Time,  calculation  of     ...   214-215 

sun 215 

Toads,  value  in  destroying  in- 
sects        ....   378 

Tobacco,  as  an  insecticide  .    .    .   375 
Tonsils,    danger    from    in- 
flammation of    ....    110-111 

Tornadoes      37 

Torricelli 6 

Toxin 109 

of  diphtheria .117 

Trade  winds 32 

Transformer,  electric 270 

Transpiration 144 

amount  of 145 

control  of 145-14G 

Transportation,  water  .  .  .  175-189 
Traps  of  waste  water  pipes  .  .171 
Tuberculosis,  transmission  of  .112 
Tungsten,  use  in  electric  light 

bulbs  .    . 269 

Typhoid  fever,  relation  to  water 

supply 173 

transmission  of 112 

vaccination  against 117 

"Typhoid  Mary"  .......   113 

Typhoons 40 

Ursa  Major,  a  constellation  .  .  206 
Ursa  Minor,  a  constellation  .  .  207 

Vaccination,  against  smallpox   .  116 
against  typhoid  fever  ....    117 


Vacuum      . 6 

of  thermos  bottle  ....  300-301 

Valleys,  origin  of .314 

Valve,  safety,  of  steam  boiler  .  306 

Variation 363 

Ventilation,  methods  of  ...  27-30 

need  for 25-27 

Vernal  equinox  212 

Vinegar,  manufacture  of  ....  125 

use  in  food  preservation  .  .  .  105 
Vitamines,  necessity  of ,  in  diet  .  343 

Vocal  cords 46 

Volt 259 

Volta,  Alessandro 257 

Voltage,  of  electric  light  wires  .  270 

Voltaic  cell 257 

Voltmeter 260 

Von  Guericke,  Otto 8 

Wall  color,  relation  to  light- 
ing ...'  285-286 

Walking,  importance  of  friction 

in 244 

Water,  composition      82 

effect  of  heat  on    ....   305-306 

erosion  by 313-314 

expansion  in  freezing    .    .    169,  312 

hard 168 

heating  by  hot  water    .    .   305-306 
use  in  righting  fire 77 

Water  pipes 168-169 

waste 171 

Water  power,   relation  to    other 

sources  of  power 154 

source  of  energy1.    .    .    .    153-155 

Water  supply,  of  New  York 

City 160-166 

Water  ways,  internal,   im- 
portance of 182-185 

Watt 261 

Watt,  James 230, 261 

Weather  Bureau       42 

Weathering,  defined 179 

production  of  soil  by    .    .   311-313 

Wedge,  an  inclined  plane    .    .    .   240 

Wells 166-168 

Westerlies,  prevailing      ....     36 

Wheel  and  axle,  as  a  simple 

machine      233-235 

Wheelbarrow     .  .  232 


INDEX 


11 


References  are  to  pages 


White  blood  corpuscles   .    .   109, 114 
Windlass,  use  in  doing  work    233-234 

Windmills 220-221 

Winds,  cyclones 36 

erosion  by 314 

prevailing  westerlies     .    .    .  33, 36 

sea  breeze 31 

tornadoes 37 

trade 32 


Winds— Continued 

use  of  energy  of  ....  220-221 

Wireless  telegraphy 262 

Work,  defined 228 

measurement  of  ....  229-230 
Wyandotte  Cave,  formation  of  .  312 


Yeast 

cause  of  fermentation 


96 
104 


YB  35750 


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